SILVERRUSH. III. Deep optical and near-infrared spectroscopy for Lyα and UV-nebular lines of bright Lyα emitters at z = 6–7

SILVERRUSH. III. Deep optical and near-infrared spectroscopy for Lyα and UV-nebular lines of... Abstract We present Lyα and UV-nebular emission line properties of bright Lyα emitters (LAEs) at z = 6–7 with a luminosity of log LLyα/[erg s−1] = 43–44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam survey data. Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 96 LAEs at z = 6–7 in SILVERRUSH. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3 σ flux limit of ∼2 × 10−18 erg s−1 for the UV-nebular emission lines of He ii λ1640, C iv λλ1548,1550, and O iii]λλ1661,1666. Except for one tentative detection of C iv, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW0) of ∼2–4 Å for C iv, He ii, and O iii] lines. We also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He ii is claimed by Sobral et al. Although two individuals and the ESO archive service carefully reanalyzed the X-SHOOTER data that are used in the study of Sobral et al., no He ii signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. The spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z ∼ 7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and the UV-continuum luminosity, which are similar to those found at z ∼ 2–3. 1 Introduction Bright Lyα-emitting galaxies are important objects in the studies of the early Universe and galaxy formation. Bright Lyα emission with log LLyα/[erg s−1] ≃ 43–44 is expected to be reproduced in various physical mechanisms (e.g., Fisher et al. 2014; Pallottini et al. 2015). Very young and metal-free stars (Population III, hereafter Pop III) hosted in galaxies would emit substantially strong Lyα radiation with a narrow He ii λ1640 line (≲200 km s−1) and a Lyα equivalent width (EW) enhancement. On the other hand, active galactic nuclei (AGNs) would also produce the bright Lyα emission with high ionization metal lines such as N v λλ1238,1240 and C iv λλ1548,1550 due to the strong UV radiation from the central ionizing source. In addition, the highly complex Lyα radiative transfer in the interstellar medium (ISM) makes it difficult to understand the Lyα emitting mechanism (e.g., Neufeld 1991; Hansen & Oh 2006). Lyα emitters (LAEs) have been surveyed by imaging observations with dedicated narrowband (NB) filters. During recent decades, the wide field of view (FoV) of Subaru/Suprime-Cam (SCam) has allowed us to identify LAE candidates at the bright end of Lyα luminosity functions (LFs; e.g., Taniguchi et al. 2005; Kashikawa et al. 2006, 2011; Shimasaku et al. 2006; Murayama et al. 2007; Ota et al. 2008; Ouchi et al. 2008, 2010; Hu et al. 2010; Konno et al. 2014; Matthee et al. 2015). Follow-up optical spectroscopic observations have confirmed several bright LAEs at z ≃ 6.6 (e.g., Himiko: Ouchi et al. 2009; CR7 and MASOSA: Sobral et al. 2015; COLA1: Hu et al. 2016; Bagley et al. 2017), and at z ≃ 5.7 (Mallery et al. 2012). However, subsequent multi-band observations have found heterogeneity in the nature of these bright LAEs. Zabl et al. (2015) have reported no detections of He ii or C iv from Himiko with VLT/X-SHOOTER. A deep ALMA observation reveals that Himiko has no strong [C ii]158 μm line and dust continuum emission (Ouchi et al. 2013). Combined with morphological properties, the bright Lyα emission of Himiko is probably caused by intense star formation in a galaxy merger. On the other hand, Sobral et al. (2015) have claimed that a narrow He ii line was detected at the 6 σ significance level from CR7 based on deep VLT/X-SHOOTER near-infrared (NIR) spectroscopy. The He ii detection might suggest that CR7 hosts Pop III stellar populations. Recently, a number of theoretical studies have discussed the strong He ii emission from CR7 (e.g., Pallottini et al. 2015; Agarwal et al. 2016; Hartwig et al. 2016; Dijkstra et al. 2016; Smidt et al. 2016; Smith et al. 2016; Visbal et al. 2016, 2017; Johnson & Dijkstra 2017; Pacucci et al. 2017). In contrast to the claim of He ii detection, CR7 clearly includes an old stellar population found from analyses of photometric data (Bowler et al. 2017), suggesting that this system is not be truly young. These studies indicate that the nature of bright LAEs has become a hot topic of debate. Even with these substantial observational and theoretical efforts, the diversity of bright LAEs has not yet been unveiled due to the limited statistics. In this paper, we present the results of our optical and NIR spectroscopic observations of bright LAEs selected with data from a new wide-FoV camera, Hyper Suprime-Cam (HSC), on the Subaru Telescope. In our spectroscopic observations, we newly identify 21 bright LAEs with log LLyα/[erg s−1] ≃ 43–44, which have enlarged the spectroscopic sample of bright LAEs by a factor of four. This is the third paper in our ongoing HSC research project for Lyα-emitting objects, Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). In this project, we study various properties of high-z LAEs, e.g., LAE clustering (Ouchi et al. 2018), photometric properties of Lyα line EW and Lyα spatial extent (Shibuya et al. 2018), spectroscopic properties of bright LAEs (this study), Lyα LFs (Konno et al. 2018), and LAE overdensity (R. Higuchi et al. in preparation). This program is one of twin programs, the other being the study of dropouts, Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH: Toshikawa et al. 2018), detailed in Ono et al. (2018) and Harikane et al. (2018). Source catalogs for the LAEs and dropouts will be presented on our project webpage.1 This paper has the following structure. In section 2, we describe the HSC data and target selections of bright LAEs for our optical and NIR spectroscopy. Section 3 presents details of the spectroscopic observations for the bright LAEs and the data reduction. In section 4, we investigate physical properties of bright LAEs at z ≃ 6 using our statistical sample of bright LAEs. In section 5, we discuss the implications for galaxy formation and evolution. We summarize our findings in section 6. Throughout this paper, we adopt the concordance cosmology with (Ωm, ΩΛ, h) = (0.3, 0.7, 0.7) (Planck Collaboration 2016). All magnitudes are given in the AB system (Oke & Gunn 1983). 2 Targets for spectroscopy 2.1 Imaging data In 2014 March, the Subaru telescope started a large-area NB survey with HSC in a Subaru strategic program (SSP: Aihara et al. 2018a). This survey will construct a sample of LAEs at z ≃ 2.2, 5.7, 6.6, and 7.3 with four NB filters: NB387, NB816, NB921, and NB101. The statistical LAE sample allows us to study the LAE evolution and physical processes of the cosmic reionization. In this study, we use the HSC SSP S16A broadband (BB: Kawanomoto et al. 2017) and NB921 and NB816 data that were obtained in 2014–2016. Note that this HSC SSP S16A data is significantly larger than the data first released in Aihara et al. (2018b). The HSC images were reduced with the HSC pipeline, hscPipe 4.0.2 (Bosch et al. 2018), which is a program from the Large Synoptic Survey Telescope (LSST) software pipeline (Ivezic et al. 2008; Axelrod et al. 2010; Jurić et al. 2015). The photometric calibration was carried out with the PanSTARRS1 processing version 2 imaging survey data (Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013). The details of the data reduction are provided in Aihara et al. (2018b), Bosch et al. (2018), and Aihara et al. (2018b). The NB921 (NB816) filter has a central wavelength of λc = 9215 Å (8177 Å) and a full width at half maximum (FWHM) of 135 Å (113 Å), which traces the redshifted Lyα emission line at z = 6.580 ± 0.056 (z = 5.726 ± 0.046). The transmission curves and the detailed specifications of these NB filters are presented in Ouchi et al. (2018). The method for transmission curve measurement is given by Kawanomoto et al. (2017). The HSC SSP S16A NB921 and NB816 data cover a total survey area of ∼21.2 and ∼13.8 deg2, respectively. The survey area consists of two UltraDeep (UD) fields, UD-COSMOS and UD-SXDS, and three Deep (D) fields, D-ELAIS-N1, D-DEEP2-3, and D-COSMOS. The FWHM of the typical seeing size is ∼ 0$${^{\prime\prime}_{.}}$$6. The 5 σ NB limiting magnitudes for the UD and D fields are typically ∼25.5 and ∼25.0 mag in a 1$${^{\prime\prime}_{.}}$$5-diameter aperture, respectively. The details of the HSC NB data are presented in Shibuya et al. (2018). This HSC NB921 and NB816 data provide the largest NB survey area for z ≃ 5.7–6.6 LAEs even before the completion of the SSP observation. 2.2 Selection of bright LAEs Using the HSC NB data, we selected targets of bright LAE candidates with log LLyα/[erg s−1] ≃ 43–44 for follow-up spectroscopic observations. The details of the LAE selection are given in Shibuya et al. (2018), but we provide a brief description here. To identify objects with an NB magnitude excess in the HSC catalog, we applied magnitude and color selection criteria similar to those of Ouchi et al. (2008, 2010). To remove spurious sources such as satellite trails and cosmic rays, we performed visual inspections of multi-band HSC images of grizy and NB for the objects selected in the magnitude and color selection criteria. We also checked multi-epoch images to remove transients and asteroid-like moving objects. In total, photometric candidates of 1153 and 1077 LAEs at z ≃ 6.6 and z ≃ 5.7 were identified in the HSC NB921 and NB816 fields, respectively. Finally, we selected bright LAE candidates with an NB magnitude of NB ≤ 24 mag, corresponding to log LLyα/[erg s−1] ≃ 43–44. 3 Spectroscopic data We carried out optical and NIR spectroscopic observations for the bright LAE candidates at z ≃ 5.7–6.6 selected with the HSC NB data. These optical and NIR observations mainly (1) make spectroscopic confirmations through Lyα, and (2) investigate properties of ionizing sources (e.g., the presence of metal-poor galaxies and AGN activity) for bright LAEs. Table 1 summarizes the instruments, the exposure time, and line flux limits of our spectroscopic observations for each target. Table 1. Our optical and NIR spectroscopic observations for bright LAEs.* Object ID  Opt. inst.  Texp,opt  flim,opt  NIR inst.  Texp,NIR  flim,NIR      (min)  (erg s−1 cm−2)    (min)  (erg s−1 cm−2)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  HSC J162126+545719  FOCAS  60  ≃1.2 × 10−18  MOSFIRE  120  ≃1.8 × 10−18  HSC J233125−005216  LDSS3  90  ≃0.5 × 10−18  —  —  —  HSC J160234+545319  FOCAS  60  ≃0.3 × 10−18  nuMOIRCS  180  ≃5.3 × 10−18  HSC J160940+541409  FOCAS  60  ≃0.6 × 10−18  nuMOIRCS  300  ≃6.0 × 10−18  HSC J100334+024546  FOCAS  100  ≃1.3 × 10−18  —  —  —  HSC J100550+023401  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.3 × 10−18  HSC J160707+555347  FOCAS  60  ≃0.5 × 10−18  —  —  —  HSC J160107+550720  FOCAS  60  ≃0.3 × 10−18  —  —  —  HSC J233408+004403  FOCAS  60  ≃0.3 × 10−18  MOSFIRE  120  ≃0.8 × 10−18  HSC J021835−042321†  —  —  —  MOSFIRE  120  ≃1.5 × 10−18  HSC J233454+003603  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.6 × 10−18  HSC J021752−053511  FOCAS  60  ≃0.1 × 10−18  —  —  —  HSC J232558+002557  FOCAS  60  ≃0.2 × 10−18  —  —  —  HSC J022001−051637  LDSS3  45  ≃0.3 × 10−18  —  —  —  Object ID  Opt. inst.  Texp,opt  flim,opt  NIR inst.  Texp,NIR  flim,NIR      (min)  (erg s−1 cm−2)    (min)  (erg s−1 cm−2)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  HSC J162126+545719  FOCAS  60  ≃1.2 × 10−18  MOSFIRE  120  ≃1.8 × 10−18  HSC J233125−005216  LDSS3  90  ≃0.5 × 10−18  —  —  —  HSC J160234+545319  FOCAS  60  ≃0.3 × 10−18  nuMOIRCS  180  ≃5.3 × 10−18  HSC J160940+541409  FOCAS  60  ≃0.6 × 10−18  nuMOIRCS  300  ≃6.0 × 10−18  HSC J100334+024546  FOCAS  100  ≃1.3 × 10−18  —  —  —  HSC J100550+023401  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.3 × 10−18  HSC J160707+555347  FOCAS  60  ≃0.5 × 10−18  —  —  —  HSC J160107+550720  FOCAS  60  ≃0.3 × 10−18  —  —  —  HSC J233408+004403  FOCAS  60  ≃0.3 × 10−18  MOSFIRE  120  ≃0.8 × 10−18  HSC J021835−042321†  —  —  —  MOSFIRE  120  ≃1.5 × 10−18  HSC J233454+003603  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.6 × 10−18  HSC J021752−053511  FOCAS  60  ≃0.1 × 10−18  —  —  —  HSC J232558+002557  FOCAS  60  ≃0.2 × 10−18  —  —  —  HSC J022001−051637  LDSS3  45  ≃0.3 × 10−18  —  —  —  *(1) Object ID, sorted by the NB magnitude. (2) Instrument for optical spectroscopy. (3) Integration time for optical spectroscopy. (4) The 1 σ line flux sensitivity near Lyα emission lines. (5) Instrument for NIR spectroscopy. (6) Integration time for NIR spectroscopy. (7) Average values of the 1 σ line flux sensitivity at the expected wavelengths of C iv, He ii, and O iii]. †Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. View Large In subsections 3.1 and 3.2, we describe the details of the optical and NIR spectroscopic data, respectively. 3.1 Optical spectroscopic data We performed optical follow-up spectroscopy for bright LAE candidates at z ≃ 5.7–6.6 to detect Lyα emission lines. The choice of targets depended on the target visibility during the allocated time for individual spectroscopic observations. Basically, we selected the brightest LAE candidates as the targets in each observing run. 3.1.1 Subaru/FOCAS We used the Faint Object Camera and Spectrograph (FOCAS: Kashikawa et al. 2002) on the Subaru telescope to observe 16 LAE candidates. Out of the 16 objects, we observed 15 LAEs on 2016 June 21–22 and September 8 (S16A-060N and S16B-029N, PI: T. Shibuya), and one as a filler target of a FOCAS observation in 2015 December (S15B-059, PI: S. Yuma; see Yuma et al. 2017). These observations were made with the VPH900 grism with the O58 order-cut filter, giving spectral coverage of 7500–10450 Å with a dispersion of 0.74 Å pix−1. The 0$${^{\prime\prime}_{.}}$$8-wide slit used gave a spectroscopic resolution of R ≃ 1800, which is sufficient to distinguish [O ii] doublet lines from low-z galaxy contaminants at z ≃ 0.6–0.8. The observing nights were photometric, with good seeing of ∼ 0$${^{\prime\prime}_{.}}$$6–1$${^{\prime\prime}_{.}}$$0. The Multi-Object Spectroscopy (MOS) mode was used to securely align the slits on our high-z sources. Each of the 20 min exposures was taken by dithering the telescope pointing along the slit by ± 1$${^{\prime\prime}_{.}}$$0. The standard star Feige 34 was taken at the beginning and end of each observed night (Massey & Gronwall 1990). Our FOCAS spectra were reduced in a standard manner with the IRAF2 package (e.g., Kashikawa et al. 2006; Shibuya et al. 2012). First, we performed flat-fielding with flat images, corrected for the image distortion, calibrated wavelengths with sky OH lines, and rejected sources illuminated by cosmic ray injections. Next, we subtracted the sky background. Then, we stacked the two-dimensional (2D) spectra. From each item of 2D data, we then extracted one-dimensional (1D) spectra using an extraction width of ∼ ±0$${^{\prime\prime}_{.}}$$4– ± 0$${^{\prime\prime}_{.}}$$8 in the spatial direction of the slits. The extraction width was determined based on the extent of the targets and the seeing conditions during the observations. Similarly, these extraction widths were used for the data obtained from the other optical and NIR spectrographs (subsections 3.1 and 3.2). Finally, we carried out flux calibrations for the 1D spectra using the data of standard stars. The slit loss of the emission line flux was automatically corrected in the flux calibration. This is because we observed the standard stars in the observing configuration (i.e., slit width) and sky condition that were the same as those for our main targets. Note that our high-z main targets are point source-like objects whose slit loss is the same as standard stars. For this reason, we did not perform data reduction procedures for slit loss correction for our optical and NIR spectra in subsections 3.1 and 3.2. 3.1.2 Magellan/LDSS3 We also used the Low Dispersion Survey Spectrograph 3 (LDSS3) on the Magellan II (Clay) telescope in October 2016 (PI: M. Rauch) to take spectroscopy for two bright LAE candidates. The seeing was ∼ 0$${^{\prime\prime}_{.}}$$6–1$${^{\prime\prime}_{.}}$$0. We set the instrumental configuration to observe wavelength ranges of 8000–10000 Å. The spatial pixel scale was 0$${^{\prime\prime}_{.}}$$189 pix−1, and the spectral dispersion was 0.47 Å pix−1. The slit width is 0$${^{\prime\prime}_{.}}$$8. 3.1.3 Magellan/IMACS In addition to the Subaru/FOCAS and Magellan/LDSS3 observations, we used spectroscopic data obtained with the Inamori-Magellan Areal Camera and Spectrograph (IMACS; Dressler et al. 2011) on the Magellan I Baade Telescope. The observations were conducted for high-z galaxies in the SXDS field in 2007–2011 (PI: M. Ouchi; R. Higuchi et al. in preparation). In the HSC LAE and IMACS catalog matching, we obtained optical spectra for eight bright LAEs. 3.1.4 LAE spectroscopic confirmations In total, we newly confirm 21 bright LAEs with a clear Lyα emission line in our Subaru/FOCAS and Magellan/LDSS3 observations and our Magellan/IMACS data. The 1D and 2D optical spectra of the 21 bright LAEs are shown in figure 1. A prominent asymmetric emission line is found at ∼9210 Å and ∼8160 Å for each LAE at z ≃ 6.6 and z ≃ 5.7, respectively. These emission lines are detected at the ∼10 σ–20 σ significance levels. No other emission line feature is found in the range of the observed wavelengths. We obtain the redshift of the bright LAEs by fitting the symmetric Gaussian profile to the observed Lyα emission lines in the wavelength ranges where the flux drops to 70% of its peak value (Shibuya et al. 2014a). Figure 2 shows the NB magnitude and Lyα EW, which is obtained in subsection 4.1. As shown in figure 2, our newly confirmed bright LAEs are as bright as, e.g., Himiko and CR7. Fig. 1. View largeDownload slide Lyα spectra for the 21 newly identified bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The red and blue lines represent the Lyα spectra of the bright LAEs at z ≃ 6.6 and ≃ 5.7, respectively. The dashed gray curves indicate the transmission curves of NB921 and NB816. The solid gray lines denote the sky OH emission lines. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. (Color online) Fig. 1. View largeDownload slide Lyα spectra for the 21 newly identified bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The red and blue lines represent the Lyα spectra of the bright LAEs at z ≃ 6.6 and ≃ 5.7, respectively. The dashed gray curves indicate the transmission curves of NB921 and NB816. The solid gray lines denote the sky OH emission lines. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. (Color online) Fig. 2. View largeDownload slide NB magnitude and Lyα EW for LAEs at z ≃ 6.6 (left) and ≃ 5.7 (right). The red squares represent the 21 newly identified bright LAEs. The green diamonds indicate NB < 24 bright LAEs which have been spectroscopically confirmed by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The magenta filled circles present LAE candidates in HSC LAE catalogs constructed by Shibuya et al. (2018). The gray open circles denote LAE candidates found in SCam NB surveys (Ouchi et al. 2008, 2010). The objects with EW0,Lyα > 700 Å are plotted at EW0,Lyα = 700 Å. (Color online) Fig. 2. View largeDownload slide NB magnitude and Lyα EW for LAEs at z ≃ 6.6 (left) and ≃ 5.7 (right). The red squares represent the 21 newly identified bright LAEs. The green diamonds indicate NB < 24 bright LAEs which have been spectroscopically confirmed by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The magenta filled circles present LAE candidates in HSC LAE catalogs constructed by Shibuya et al. (2018). The gray open circles denote LAE candidates found in SCam NB surveys (Ouchi et al. 2008, 2010). The objects with EW0,Lyα > 700 Å are plotted at EW0,Lyα = 700 Å. (Color online) We also check whether our LAEs selected with the HSC data, HSC LAEs, are spectroscopically confirmed in previous studies for the COSMOS and SXDS fields (Murayama et al. 2007; Ouchi et al. 2008, 2010; Taniguchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). In spectroscopic samples obtained by the previous studies, we find 7 bright LAEs with NB < 24 mag and 69 faint ones with NB > 24 mag. In total, 96 LAEs are confirmed in our spectroscopic observations and the previous studies. Table 2 summarizes the number of spectroscopically confirmed HSC LAEs. Table 2. Number of spectroscopically confirmed HSC LAEs at z ≃ 5.7–6.6.* Sample  NLAE,spec  Spec. obs. or sample  (1)  (2)  (3)  Bright (NB < 24)  13  FOCAS, LDSS3  Bright (NB < 24)  8  IMACS  Bright (NB < 24)  7  Literature‡  Faint (NB > 24)†  68  LDSS3, IMACS, literature‡  Total  96  —  Sample  NLAE,spec  Spec. obs. or sample  (1)  (2)  (3)  Bright (NB < 24)  13  FOCAS, LDSS3  Bright (NB < 24)  8  IMACS  Bright (NB < 24)  7  Literature‡  Faint (NB > 24)†  68  LDSS3, IMACS, literature‡  Total  96  —  *(1) LAE sample. (2) Number of spectroscopically confirmed LAEs. (3) Instruments for observations and spectroscopic samples. †See tables 8 and 9 in the Appendix. ‡Murayama et al. (2007), Ouchi et al. (2008, 2010), Taniguchi et al. (2009), Mallery et al. (2012), Sobral et al. (2015), Hu et al. (2016). View Large The photometric properties and the HSC images for the bright LAEs are given in table 3 and figure 3, respectively. Although most of the bright LAEs are not detected in the blue bands of g and r, COLA1 is marginally detected in the r-band image at ∼2.5 σ. Fig. 3. View largeDownload slide HSC cutout images of the spectroscopically confirmed bright LAEs with NB < 24 mag at z ≃ 6.6 (left) and ≃ 5.7 (right). The seven objects at the bottom are the previously identified bright LAEs at z ≃ 6.6 (Ouchi et al. 2009; Sobral et al. 2015; Hu et al. 2016) and at z ≃ 5.7 (Mallery et al. 2012). The image size is 4″ × 4″. The scale of the flux density is arbitrary. (Color online) Fig. 3. View largeDownload slide HSC cutout images of the spectroscopically confirmed bright LAEs with NB < 24 mag at z ≃ 6.6 (left) and ≃ 5.7 (right). The seven objects at the bottom are the previously identified bright LAEs at z ≃ 6.6 (Ouchi et al. 2009; Sobral et al. 2015; Hu et al. 2016) and at z ≃ 5.7 (Mallery et al. 2012). The image size is 4″ × 4″. The scale of the flux density is arbitrary. (Color online) Table 3. Photometric properties of bright LAEs with spectroscopic redshifts.* Object ID  α (J2000.0)  δ (J2000.0)  zLyα  NB  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  NB921 (z ≃ 6.6)  HSC J162126+545719  16:21:26.51  +54:57:19.14  6.545  22.33 ± 0.02  >25.8  23.77 ± 0.18  22.92 ± 0.16  HSC J233125−005216  23:31:25.36  −00:52:16.36  6.559  23.17 ± 0.08  >26.6  25.34 ± 0.27  24.96 ± 0.37  HSC J160234+545319  16:02:34.77  +54:53:19.95  6.576  23.24 ± 0.05  >26.4  24.79 ± 0.26  >24.8  HSC J160940+541409  16:09:40.25  +54:14:09.04  6.564  23.52 ± 0.06  >26.4  25.45 ± 0.32  >24.7  HSC J100334+024546  10:03:34.66  +02:45:46.56  6.575  23.61 ± 0.05  >26.7  25.62 ± 0.27  24.97 ± 0.29  HSC J100550+023401  10:05:50.97  +02:34:01.51  6.573  23.71 ± 0.10  >26.4  25.15 ± 0.22  >25.3  HSC J160707+555347  16:07:07.48  +55:53:47.90  6.586  23.86 ± 0.09  >26.5  25.35 ± 0.32  >24.8  HSC J160107+550720  16:01:07.45  +55:07:20.63  6.563  23.96 ± 0.12  >26.4  >25.5  >24.4  NB816 (z ≃ 5.7)  HSC J233408+004403  23:34:08.79  +00:44:03.78  5.707  22.85 ± 0.04  25.40 ± 0.20  >25.8  >25.1  HSC J021835−042321†  02:18:35.94  −04:23:21.62  5.757  23.10 ± 0.06  25.38 ± 0.22  24.93 ± 0.19  25.23 ± 0.56  HSC J233454+003603  23:34:54.95  +00:36:03.99  5.732  23.16 ± 0.05  25.42 ± 0.19  25.60 ± 0.37  24.59 ± 0.28  HSC J021752−053511  02:17:52.63  −05:35:11.78  5.756  23.17 ± 0.05  25.24 ± 0.12  24.50 ± 0.14  24.42 ± 0.20  HSC J021828−051423†  02:18:28.87  −05:14:23.01  5.737  23.57 ± 0.04  26.25 ± 0.22  26.27 ± 0.38  >25.78  HSC J021724−053309†  02:17:24.02  −05:33:09.61  5.707  23.64 ± 0.08  >25.8  25.36 ± 0.29  >25.4  HSC J021859−052916†  02:18:59.92  −05:29:16.81  5.674  23.71 ± 0.06  25.17 ± 0.14  24.05 ± 0.09  24.00 ± 0.17  HSC J021836−053528†  02:18:36.37  −05:35:28.07  5.700  23.75 ± 0.06  25.95 ± 0.22  25.20 ± 0.21  24.88 ± 0.25  HSC J232558+002557  23:25:58.43  +00:25:57.53  5.703  23.78 ± 0.09  25.86 ± 0.22  25.29 ± 0.28  >24.9  HSC J022001−051637  02:20:01.10  −05:16:37.51  5.708  23.79 ± 0.04  26.04 ± 0.19  25.99 ± 0.30  >25.8  HSC J021827−044736†  02:18:27.44  −04:47:36.98  5.703  23.80 ± 0.08  26.93 ± 0.38  >26.3  >25.8  HSC J021830−051457†  02:18:30.53  −05:14:57.81  5.688  23.83 ± 0.05  25.93 ± 0.17  26.27 ± 0.38  >25.8  HSC J021624−045516†  02:16:24.70  −04:55:16.55  5.706  23.94 ± 0.06  26.24 ± 0.22  25.67 ± 0.23  >25.5  Previously identified bright LAEs  HSC J100235+021213†  10:02:35.38  +02:12:13.96  6.593  23.18 ± 0.03  >26.9  24.98 ± 0.12  25.29 ± 0.31  HSC J100058+014815§  10:00:58.00  +01:48:15.14  6.604  23.25 ± 0.03  >26.9  25.12 ± 0.13  24.48 ± 0.16  HSC J021757−050844‖  02:17:57.58  −05:08:44.63  6.595  23.50 ± 0.03  >27.4  25.77 ± 0.20  25.40 ± 0.27  HSC J100124+023145♯  10:01:24.79  +02:31:45.38  6.541  23.61 ± 0.03  >27.0  25.25 ± 0.14  25.64 ± 0.40  HSC J100109+021513**  10:01:09.72  +02:15:13.45  5.712  23.13 ± 0.02  25.77 ± 0.13  25.91 ± 0.21  25.97 ± 0.41  HSC J100129+014929**  10:01:29.07  +01:49:29.81  5.707  23.47 ± 0.02  25.87 ± 0.15  25.27 ± 0.13  25.30 ± 0.28  HSC J100123+015600**  10:01:23.84  +01:56:00.46  5.726  23.94 ± 0.03  26.43 ± 0.25  25.85 ± 0.21  >25.9  Object ID  α (J2000.0)  δ (J2000.0)  zLyα  NB  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  NB921 (z ≃ 6.6)  HSC J162126+545719  16:21:26.51  +54:57:19.14  6.545  22.33 ± 0.02  >25.8  23.77 ± 0.18  22.92 ± 0.16  HSC J233125−005216  23:31:25.36  −00:52:16.36  6.559  23.17 ± 0.08  >26.6  25.34 ± 0.27  24.96 ± 0.37  HSC J160234+545319  16:02:34.77  +54:53:19.95  6.576  23.24 ± 0.05  >26.4  24.79 ± 0.26  >24.8  HSC J160940+541409  16:09:40.25  +54:14:09.04  6.564  23.52 ± 0.06  >26.4  25.45 ± 0.32  >24.7  HSC J100334+024546  10:03:34.66  +02:45:46.56  6.575  23.61 ± 0.05  >26.7  25.62 ± 0.27  24.97 ± 0.29  HSC J100550+023401  10:05:50.97  +02:34:01.51  6.573  23.71 ± 0.10  >26.4  25.15 ± 0.22  >25.3  HSC J160707+555347  16:07:07.48  +55:53:47.90  6.586  23.86 ± 0.09  >26.5  25.35 ± 0.32  >24.8  HSC J160107+550720  16:01:07.45  +55:07:20.63  6.563  23.96 ± 0.12  >26.4  >25.5  >24.4  NB816 (z ≃ 5.7)  HSC J233408+004403  23:34:08.79  +00:44:03.78  5.707  22.85 ± 0.04  25.40 ± 0.20  >25.8  >25.1  HSC J021835−042321†  02:18:35.94  −04:23:21.62  5.757  23.10 ± 0.06  25.38 ± 0.22  24.93 ± 0.19  25.23 ± 0.56  HSC J233454+003603  23:34:54.95  +00:36:03.99  5.732  23.16 ± 0.05  25.42 ± 0.19  25.60 ± 0.37  24.59 ± 0.28  HSC J021752−053511  02:17:52.63  −05:35:11.78  5.756  23.17 ± 0.05  25.24 ± 0.12  24.50 ± 0.14  24.42 ± 0.20  HSC J021828−051423†  02:18:28.87  −05:14:23.01  5.737  23.57 ± 0.04  26.25 ± 0.22  26.27 ± 0.38  >25.78  HSC J021724−053309†  02:17:24.02  −05:33:09.61  5.707  23.64 ± 0.08  >25.8  25.36 ± 0.29  >25.4  HSC J021859−052916†  02:18:59.92  −05:29:16.81  5.674  23.71 ± 0.06  25.17 ± 0.14  24.05 ± 0.09  24.00 ± 0.17  HSC J021836−053528†  02:18:36.37  −05:35:28.07  5.700  23.75 ± 0.06  25.95 ± 0.22  25.20 ± 0.21  24.88 ± 0.25  HSC J232558+002557  23:25:58.43  +00:25:57.53  5.703  23.78 ± 0.09  25.86 ± 0.22  25.29 ± 0.28  >24.9  HSC J022001−051637  02:20:01.10  −05:16:37.51  5.708  23.79 ± 0.04  26.04 ± 0.19  25.99 ± 0.30  >25.8  HSC J021827−044736†  02:18:27.44  −04:47:36.98  5.703  23.80 ± 0.08  26.93 ± 0.38  >26.3  >25.8  HSC J021830−051457†  02:18:30.53  −05:14:57.81  5.688  23.83 ± 0.05  25.93 ± 0.17  26.27 ± 0.38  >25.8  HSC J021624−045516†  02:16:24.70  −04:55:16.55  5.706  23.94 ± 0.06  26.24 ± 0.22  25.67 ± 0.23  >25.5  Previously identified bright LAEs  HSC J100235+021213†  10:02:35.38  +02:12:13.96  6.593  23.18 ± 0.03  >26.9  24.98 ± 0.12  25.29 ± 0.31  HSC J100058+014815§  10:00:58.00  +01:48:15.14  6.604  23.25 ± 0.03  >26.9  25.12 ± 0.13  24.48 ± 0.16  HSC J021757−050844‖  02:17:57.58  −05:08:44.63  6.595  23.50 ± 0.03  >27.4  25.77 ± 0.20  25.40 ± 0.27  HSC J100124+023145♯  10:01:24.79  +02:31:45.38  6.541  23.61 ± 0.03  >27.0  25.25 ± 0.14  25.64 ± 0.40  HSC J100109+021513**  10:01:09.72  +02:15:13.45  5.712  23.13 ± 0.02  25.77 ± 0.13  25.91 ± 0.21  25.97 ± 0.41  HSC J100129+014929**  10:01:29.07  +01:49:29.81  5.707  23.47 ± 0.02  25.87 ± 0.15  25.27 ± 0.13  25.30 ± 0.28  HSC J100123+015600**  10:01:23.84  +01:56:00.46  5.726  23.94 ± 0.03  26.43 ± 0.25  25.85 ± 0.21  >25.9  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5) Total magnitudes of NB921 for z ≃ 6.6 LAEs and NB816 for z ≃ 5.7 LAEs. (6)–(8) Total magnitudes of i, z, and y bands. (6)–(8) 2 σ limiting magnitudes for undetected bands. †Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. †COLA1 in Hu et al. (2016). §CR7 in Sobral et al. (2015). ‖Himiko in Ouchi et al. (2009). ♯MASOSA in Sobral et al. (2015). **Spectroscopically confirmed in Mallery et al. (2012). View Large Combining our 21 newly identified and the 7 previously confirmed bright LAEs (i.e., Himiko, CR7, MASOSA, COLA1, and three z ≃ 5.7 objects from Mallery et al. 2012), we have constructed a sample of 28 bright LAEs. The HSC data and our observations have enlarged a spectroscopic sample of bright LAEs by a factor of four. The large sample allows for a statistical study on the physical properties of bright LAEs with log LLyα/[erg s−1] ≃ 43–44. 3.1.5 Contamination rates in the LAE candidates We estimate contamination rates, fcontami, in the HSC LAE candidates using the spectroscopic data. In our Subaru/FOCAS and Magellan/LDSS3 observations for 12 z ≃ 6.6 and 6 z ≃ 5.7 bright LAE candidates with NB <24 mag, we identify 4 and 1 low-z contaminants, respectively. Figure 4 presents the spectra and HSC cutout images for the low-z contaminants. All of the five contaminants are strong [O iii]λλ4959, 5007 emitters at z ≃ 0.6–0.8 with faint BB magnitudes. The Hβ and Hγ emission lines are not significantly detected in the short integration times (i.e., ≃ 20–40 min) of the FOCAS and LDSS3 observations. The photometric properties of these low-z contaminants are listed in table 4. We find that fcontami ≃ 33% (=4/12) and ≃ 17% (=1/6) for bright LAE candidates with NB < 24 mag at z ≃ 6.6 and z ≃ 5.7, respectively. Fig. 4. View largeDownload slide (Left) Spectra for the five low-z contaminants in the Subaru/FOCAS and Magellan/LDSS3 observations. The red arrows indicate the positions of [O iii]λλ4959,5007 emission lines. The dashed gray curves denote the transmission curves of NB921 and NB816. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. The y-axis represents the flux density in arbitrary units. (Right) HSC cutout images of the low-z contaminants. The image size is 4″ × 4″. The scale of the flux density is arbitrary. The photometric properties of the low-z contaminants are summarized in table 4. (Color online) Fig. 4. View largeDownload slide (Left) Spectra for the five low-z contaminants in the Subaru/FOCAS and Magellan/LDSS3 observations. The red arrows indicate the positions of [O iii]λλ4959,5007 emission lines. The dashed gray curves denote the transmission curves of NB921 and NB816. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. The y-axis represents the flux density in arbitrary units. (Right) HSC cutout images of the low-z contaminants. The image size is 4″ × 4″. The scale of the flux density is arbitrary. The photometric properties of the low-z contaminants are summarized in table 4. (Color online) Table 4. Low-z contamination sources.* Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB  g  r  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10)  NB921  HSC J1001+0229  10:01:44.34  +02:29:09.96  0.840  23.64  26.78  >26.7  >26.5  25.10  >25.0  HSC J0957+0306  09:57:16.07  +03:06:30.31  0.841  23.73  >27.2  >26.7  >26.5  25.15  >25.0  HSC J1611+5541  16:11:30.34  +55:41:00.39  0.844  23.82  >27.2  >26.7  26.37  25.47  >25.0  HSC J1609+5620  16:09:18.03  +56:20:50.89  0.838  23.96  >27.2  >26.7  >26.5  25.52  >25.0  NB816  HSC J2327+0054  23:27:48.16  +00:54:20.84  0.639  23.18  >27.2  >26.7  25.31  >25.8  >25.0  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB  g  r  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10)  NB921  HSC J1001+0229  10:01:44.34  +02:29:09.96  0.840  23.64  26.78  >26.7  >26.5  25.10  >25.0  HSC J0957+0306  09:57:16.07  +03:06:30.31  0.841  23.73  >27.2  >26.7  >26.5  25.15  >25.0  HSC J1611+5541  16:11:30.34  +55:41:00.39  0.844  23.82  >27.2  >26.7  26.37  25.47  >25.0  HSC J1609+5620  16:09:18.03  +56:20:50.89  0.838  23.96  >27.2  >26.7  >26.5  25.52  >25.0  NB816  HSC J2327+0054  23:27:48.16  +00:54:20.84  0.639  23.18  >27.2  >26.7  25.31  >25.8  >25.0  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift. (5) Total magnitudes of NB921 for z ≃ 6.6 LAEs and NB816 for z ≃ 5.7 LAEs. (6)–(10) Total magnitudes of g, r, i, z, and y bands. (6)–(10) 2 σ limiting magnitudes for undetected bands. View Large We also calculate fcontami in the HSC LAE candidates including our Magellan/IMACS spectroscopic data (sub-subsection 3.1.3). This spectroscopic sample includes faint HSC LAE candidates with NB > 24 mag. Combining our Subaru/FOCAS and Magellan/LDSS3 data and the cross-matching of the Magellan/IMACS spectroscopic catalogs, we find that 28 and 53 HSC LAE candidates at z ≃ 6.6 and z ≃ 5.7 are spectroscopically observed. In total, we find that 4 out of 28 (4 out of 53) HSC LAE candidates are low-z contaminants, and estimate fcontami to be ≃ 14% and ≃ 8% for the samples of z ≃ 6.6 and z ≃ 5.7 LAEs, respectively. In these estimates with the spectroscopic data, we find that fcontami ≃ 0%–30%. Table 5 summarizes the contamination rates. These fcontami values are used for the contamination correction for, e.g., LAE clustering (Ouchi et al. 2018), Lyα LFs (Konno et al. 2018), and LAE overdensity (R. Higuchi et al. in preparation). Table 5. Contamination rates in the HSC LAE candidates.* Redshift  Nobs  Nlow-z  fcontami  Spec. obs.  (1)  (2)  (3)  (4)  (5)  Bright (NB < 24)  6.6  12  4  0.33  FOCAS,† LDSS3†  5.7  6  1  0.17  FOCAS,† LDSS3†  All  6.6  28  4  0.14  FOCAS,† LDSS3,†,‡ IMACS§  5.7  53  4  0.08  FOCAS,† LDSS3,† IMACS§  Redshift  Nobs  Nlow-z  fcontami  Spec. obs.  (1)  (2)  (3)  (4)  (5)  Bright (NB < 24)  6.6  12  4  0.33  FOCAS,† LDSS3†  5.7  6  1  0.17  FOCAS,† LDSS3†  All  6.6  28  4  0.14  FOCAS,† LDSS3,†,‡ IMACS§  5.7  53  4  0.08  FOCAS,† LDSS3,† IMACS§  *(1) Redshift of the LAE sample. (2) Number of spectroscopically observed HSC LAEs. (3) Number of low-z contaminants. (4) Contamination rates. (5) Spectroscopic follow-up observations. Only for the observations whose Nobs and Nlow-z are found. †This study. ‡Y. Harikane et al. (in preparation.) §R. Higuchi (in preparation). View Large 3.2 NIR spectroscopic data We performed deep NIR spectroscopy to investigate whether the rest-frame UV-nebular emission lines (i.e., C iv λλ1548, 1550, He ii λ1640, and O iii]λλ1661,1666) exist in bright LAEs. As a first attempt, we observed 7 out of the spectroscopically confirmed 21 bright LAEs. The LAEs observed by NIR spectrographs are listed in table 1. The choice of targets depended on the target visibility during the allocated time for the individual spectroscopic observations. Basically, we have selected the brightest LAEs as the targets in each observing run. 3.2.1 Keck/MOSFIRE We used the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE: McLean et al. 2012) on the Keck I telescope to observe four LAEs on 2016 September 9 (S16B-029N, PI: T. Shibuya) and an LAE on 2015 January 3–4 as a filler target (S15B-075, PI: M. Ouchi). Similar to the Subaru/FOCAS observations, the MOS mode was utilized to securely align the slits on our high-z sources. We used the Y- and J-band filters for LAEs at z ≃ 5.7 and z ≃ 6.6, respectively. The seeing size was ∼ 0$${^{\prime\prime}_{.}}$$5–0$${^{\prime\prime}_{.}}$$6. The 0$${^{\prime\prime}_{.}}$$8-wide slit was used, giving a spectral resolution of R ≃ 3500. The data for objects and standard stars were reduced using the MOSFIRE data reduction pipeline.3 We conducted standard reduction processes for the MOSFIRE spectra with sets of default pipeline parameters (see, e.g., Kojima et al. 2016). Using spectral type A stars which were taken in this observing run, we performed flux calibrations for the spectra of the target LAEs. 3.2.2 Subaru/nuMOIRCS We used the upgraded version of the Multi-Object InfraRed Camera and Spectrograph (nuMOIRCS; Ichikawa et al. 2006; Suzuki et al. 2008; Fabricius et al. 2016; Walawender et al. 2016) on the Subaru telescope on 2016 June 21–22 to observe two LAEs at z ≃ 6.6 (S16A-060N, PI: T. Shibuya). The MOS mode was used to securely align the slits on our high-z sources. There were thin sky cirrus clouds, but the weather conditions were photometric. The seeing size was ∼ 0$${^{\prime\prime}_{.}}$$5–1$${^{\prime\prime}_{.}}$$0. The width of each slit in the MOS masks is 0$${^{\prime\prime}_{.}}$$8. We used the VPH-J grism, giving a spectral resolution of R ≃ 3000. The standard star HIP115119 was observed on each night for flux calibrations. We reduced the nuMOIRCS spectra with IRAF in a manner similar to the FOCAS data reduction (sub-subsection 3.1.1). We performed bias subtraction, flat-fielding, image distortion correction, cosmic ray rejection, wavelength calibration, sky subtraction, and flux calibration. 4 Results 4.1 Physical properties We present the physical quantities related to the Lyα emission: Lyα flux, fLyα, Lyα luminosity, LLyα, and the rest-frame Lyα EW, EW0,Lyα, for the bright LAEs with a spectroscopic redshift. To obtain these quantities, we scale the observed Lyα spectra to match the NB and BB magnitudes. Here we assume the rest-frame UV spectral slope of β = −2. The β parameter is defined by fλ ∝ λβ, where fλ is a galaxy spectrum at ≃1500–3000 Å. The 2 σ lower limits of y- (z)-band magnitudes are used for z ≃ 6.6 (z ≃ 5.7) LAEs whose UV continuum emission is not detected. For HSC J162126+545719, whose UV continuum is detected in the spectroscopic data (see figure 1), we use the UV continuum flux density in the spectra to measure the EW0,Lyα and MUV values. Table 6 presents the quantities of fLyα, LLyα, and EW0,Lyα for our 21 bright LAEs, including a sample of 7 LAEs identified by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). Figure 2 shows EW0,Lyα as a function of NB magnitude. The EW0,Lyα value ranges from ≃ 10 Å to ≃ 300 Å. Table 6. Physical properties of bright LAEs with spectroscopic redshifts. Object ID  FLyα  log LLyα  EW0,Lyα  ΔVFWHM  MUV  Extended?†    (erg s−1 cm−2)  (erg s−1)  (Å)  (km s−1)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J162126+545719  16.0 ± 0.12  43.89 ± 0.12  98.6 ± 32.7§ §  367 ± 19  −20.48 ± 0.31§ §    HSC J233125−005216  8.20 ± 0.05  43.60 ± 0.15  80.8 ± 33.4  168 ± 17  −21.87 ± 0.37    HSC J160234+545319  6.74 ± 0.03  43.52 ± 0.002  >57.3  394 ± 21  >−22.0    HSC J160940+541409  3.98 ± 0.06  43.29 ± 0.006  >30.8  302 ± 29  >−22.1  Y  HSC J100334+024546  6.14 ± 0.13  43.48 ± 0.18  61.1 ± 18.9  239 ± 18  −21.87 ± 0.29    HSC J100550+023401  7.94 ± 0.10  43.59 ± 0.005  >107.0  312 ± 34  >−21.5    HSC J160707+555347  6.07 ± 0.05  43.48 ± 0.004  >51.5  397 ± 30  >−22.0    HSC J160107+550720  2.45 ± 0.03  43.08 ± 0.005  >14.4  393 ± 33  >−22.4    NB816 (z ≃ 5.7)  HSC J233408+004403  13.5 ± 0.03  43.68 ± 0.001  >256.4  323 ± 18  >−20.8    HSC J021835−042321†  12.5 ± 0.07  43.66 ± 0.08  107.4 ± 21.4  298 ± 34  −21.70 ± 0.19    HSC J233454+003603  13.6 ± 0.10  43.69 ± 0.14  216.6 ± 88.5  318 ± 19  −21.02 ± 0.37    HSC J021752−053511  12.7 ± 0.09  43.66 ± 0.06  73.5 ± 10.7  157 ± 8  −22.13 ± 0.14    HSC J021828−051423†  7.04 ± 0.06  43.40 ± 0.15  207.3 ± 87.2  <410  −20.35 ± 0.38    HSC J021724−053309†  5.48 ± 0.02  43.29 ± 0.12  69.5 ± 21.9  <410  −21.25 ± 0.29    HSC J021859−052916†  4.55 ± 0.05  43.20 ± 0.04  17.2 ± 1.8  311 ± 44  −22.55 ± 0.09    HSC J021836−053528†  4.90 ± 0.03  43.24 ± 0.09  53.6 ± 11.8  <410  −21.41 ± 0.21    HSC J232558+002557  3.59 ± 0.02  43.10 ± 0.12  42.7 ± 13.1  373 ± 31  −21.32 ± 0.28    HSC J022001−051637  5.10 ± 0.03  43.26 ± 0.12  115.6 ± 37.1  271 ± 30  −20.62 ± 0.30    HSC J021827−044736†  5.34 ± 0.05  43.28 ± 0.03  >160.8  <410  >−20.3    HSC J021830−051457†  7.19 ± 0.13  43.40 ± 0.15  210.3 ± 88.8  <410  −20.34 ± 0.38    HSC J021624−045516†  4.17 ± 0.03  43.17 ± 0.09  70.5 ± 17.1  <410  −20.94 ± 0.23    Previously identified bright LAEs§  HSC J100235+021213‖  16.0  43.9  53  194  −21.55 ± 0.31    HSC J100058+014815♯  12.7 ± 0.08  43.8  211  266  −22.37 ± 0.16  Y  HSC J021757−050844**  5.06 ± 0.32  43.4  78  251  −21.44 ± 0.27  Y  HSC J100124+023145††  5.16  43.4  >206  386  −21.19 ± 0.40    HSC J100109+021513‡‡  7.32 ± 0.85  43.4  $$19.7^{+9.00}_{-7.93}$$  265 ± 71  −20.64 ± 0.41  Y  HSC J100129+014929‡‡  5.77 ± 0.61  43.3  $$60.9^{+5.89}_{-41.32}$$  422 ± 120  −21.31 ± 0.28  Y  HSC J100123+015600‡‡  3.79 ± 0.66  43.1  $$11.4^{+8.01}_{-7.32}$$  237 ± 58  >−20.72    Object ID  FLyα  log LLyα  EW0,Lyα  ΔVFWHM  MUV  Extended?†    (erg s−1 cm−2)  (erg s−1)  (Å)  (km s−1)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J162126+545719  16.0 ± 0.12  43.89 ± 0.12  98.6 ± 32.7§ §  367 ± 19  −20.48 ± 0.31§ §    HSC J233125−005216  8.20 ± 0.05  43.60 ± 0.15  80.8 ± 33.4  168 ± 17  −21.87 ± 0.37    HSC J160234+545319  6.74 ± 0.03  43.52 ± 0.002  >57.3  394 ± 21  >−22.0    HSC J160940+541409  3.98 ± 0.06  43.29 ± 0.006  >30.8  302 ± 29  >−22.1  Y  HSC J100334+024546  6.14 ± 0.13  43.48 ± 0.18  61.1 ± 18.9  239 ± 18  −21.87 ± 0.29    HSC J100550+023401  7.94 ± 0.10  43.59 ± 0.005  >107.0  312 ± 34  >−21.5    HSC J160707+555347  6.07 ± 0.05  43.48 ± 0.004  >51.5  397 ± 30  >−22.0    HSC J160107+550720  2.45 ± 0.03  43.08 ± 0.005  >14.4  393 ± 33  >−22.4    NB816 (z ≃ 5.7)  HSC J233408+004403  13.5 ± 0.03  43.68 ± 0.001  >256.4  323 ± 18  >−20.8    HSC J021835−042321†  12.5 ± 0.07  43.66 ± 0.08  107.4 ± 21.4  298 ± 34  −21.70 ± 0.19    HSC J233454+003603  13.6 ± 0.10  43.69 ± 0.14  216.6 ± 88.5  318 ± 19  −21.02 ± 0.37    HSC J021752−053511  12.7 ± 0.09  43.66 ± 0.06  73.5 ± 10.7  157 ± 8  −22.13 ± 0.14    HSC J021828−051423†  7.04 ± 0.06  43.40 ± 0.15  207.3 ± 87.2  <410  −20.35 ± 0.38    HSC J021724−053309†  5.48 ± 0.02  43.29 ± 0.12  69.5 ± 21.9  <410  −21.25 ± 0.29    HSC J021859−052916†  4.55 ± 0.05  43.20 ± 0.04  17.2 ± 1.8  311 ± 44  −22.55 ± 0.09    HSC J021836−053528†  4.90 ± 0.03  43.24 ± 0.09  53.6 ± 11.8  <410  −21.41 ± 0.21    HSC J232558+002557  3.59 ± 0.02  43.10 ± 0.12  42.7 ± 13.1  373 ± 31  −21.32 ± 0.28    HSC J022001−051637  5.10 ± 0.03  43.26 ± 0.12  115.6 ± 37.1  271 ± 30  −20.62 ± 0.30    HSC J021827−044736†  5.34 ± 0.05  43.28 ± 0.03  >160.8  <410  >−20.3    HSC J021830−051457†  7.19 ± 0.13  43.40 ± 0.15  210.3 ± 88.8  <410  −20.34 ± 0.38    HSC J021624−045516†  4.17 ± 0.03  43.17 ± 0.09  70.5 ± 17.1  <410  −20.94 ± 0.23    Previously identified bright LAEs§  HSC J100235+021213‖  16.0  43.9  53  194  −21.55 ± 0.31    HSC J100058+014815♯  12.7 ± 0.08  43.8  211  266  −22.37 ± 0.16  Y  HSC J021757−050844**  5.06 ± 0.32  43.4  78  251  −21.44 ± 0.27  Y  HSC J100124+023145††  5.16  43.4  >206  386  −21.19 ± 0.40    HSC J100109+021513‡‡  7.32 ± 0.85  43.4  $$19.7^{+9.00}_{-7.93}$$  265 ± 71  −20.64 ± 0.41  Y  HSC J100129+014929‡‡  5.77 ± 0.61  43.3  $$60.9^{+5.89}_{-41.32}$$  422 ± 120  −21.31 ± 0.28  Y  HSC J100123+015600‡‡  3.79 ± 0.66  43.1  $$11.4^{+8.01}_{-7.32}$$  237 ± 58  >−20.72    *(1) Object ID. (2) Lyα flux in units of 10−17 erg s−1 cm−2. (3) Lyα luminosity. (4) Lyα EW. (5) Velocity FWHM of the Lyα emission line. (6) Absolute UV magnitude. (7) Flag of the Lyα spatial extent. †If the column is Y, the object is spatially extended in Lyα. See Shibuya et al. (2018). ‡Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. §Physical quantities in the columns (2)–(5) are obtained from the literature. ‖COLA1 in Hu et al. (2016). ♯CR7 in Sobral et al. (2015). **Himiko in Ouchi et al. (2009). ††MASOSA in Sobral et al. (2015). ‡‡Spectroscopically confirmed in Mallery et al. (2012). §§These values are calculated from the rest-frame UV continuum emission detected in the spectroscopic data. View Large Table 6 also shows whether the bright LAEs are spatially extended or not in Lyα based on our measurements of isophotal areas, Aiso (see Shibuya et al. 2018). We find that only 5 out of the 28 bright LAEs show spatially extended Lyα emission. The Aiso measurements indicate that Lyα emission of bright LAEs is typically compact. 4.2 Lyα line width To quantify the Lyα line profiles, we measure the FWHM velocity width, ΔVFWHM. We fit the symmetric Gaussian profile to the Lyα emission lines, and obtain the observed FWHM velocity width, ΔVobs, in the same manner as in Ouchi et al. (2010) for consistency. We correct for the instrumental broadening of line profile, and obtain ΔVFWHM by $$\Delta V_{\rm FWHM}=\sqrt{\Delta V_{\rm obs}^2 - \Delta V_{\rm inst}^2}$$, where ΔVobs and ΔVinst are the FWHM velocity widths for the observed Lyα lines and the instrumental resolution, respectively. We use the uncertainties in the χ2 minimization fit as the ΔVFWHM errors. The ΔVFWHM values are listed in table 6. Figure 5 presents ΔVFWHM as a function of LLyα. We find that the bright LAEs have ΔVFWHM ≃ 200–400 km s−1, similar to z ≃ 6 faint LAEs with log LLyα/[erg s−1] ≲ 43 (Ouchi et al. 2010). The narrow Lyα emission lines of ΔV ≃ 200–400 km s−1 indicate that the bright LAEs are not broad-line AGNs. Fig. 5. View largeDownload slide Lyα line FWHM as a function of Lyα luminosity. The red filled and open squares indicate our bright LAEs with Lyα emission line spectroscopically resolved and not resolved, respectively. The green filled diamonds denote bright LAEs which have been previously confirmed (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The black circles represent faint z ≃ 6.6 LAEs with log LLyα/[erg s−1] ≲ 43 in Ouchi et al. (2010). (Color online) Fig. 5. View largeDownload slide Lyα line FWHM as a function of Lyα luminosity. The red filled and open squares indicate our bright LAEs with Lyα emission line spectroscopically resolved and not resolved, respectively. The green filled diamonds denote bright LAEs which have been previously confirmed (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The black circles represent faint z ≃ 6.6 LAEs with log LLyα/[erg s−1] ≲ 43 in Ouchi et al. (2010). (Color online) To quantify the relation between ΔVFWHM and LLyα in figure 5, we carry out Spearman rank correlation tests. In this test, we find a marginal correlation at the ∼1.7 σ significance level, possibly suggesting that ΔVFWHM increases with increasing LLyα. 4.3 X-ray, mid-IR, and radio detectability We check X-ray, mid-IR (MIR), and radio data to investigate whether the bright LAEs have a signature of AGN activities. Such X-ray, MIR, and radio data are available in the UD fields, UD-COSMOS and UD-SXDS. In UD-COSMOS, one object (i.e., HSC J100334+024546) is covered by MIR and radio data. In UD-SXDS, all ten objects are observed in X-ray, MIR, and radio. For the X-ray data, we use the XMM-Newton source catalog whose sensitivity limit is f0.5–2 keV = 6 × 10 − 16 erg cm−2 s−1 (Ueda et al. 2008). For the MIR data, we use the Spitzer/MIPS 24 μm source catalogs for UD-COSMOS (Sanders et al. 2007) and UD-SXDS (the SpUDS survey, PI: J. Dunlop). These Spitzer/MIPS 24 μm images reach 5 σ sensitivity limits of 21.2 mag in UD-COSMOS and 18.0 mag in UD-SXDS. For the radio data, we check the Very Large Array (VLA) 1.4 GHz source catalogs of Schinnerer et al. (2007) for UD-COSMOS and Simpson et al. (2006) for UD-SXDS. The typical r.m.s. noise level of the VLA data is f1.4 GHz ≃ 10 μJy beam−1. We find that there are no counterparts in the X-ray, MIR, and radio data, indicating that there is no clear signature of AGN activities based on the multi-wavelength data. By considering the typical spectral energy distribution of AGNs (e.g., Elvis et al. 1994; Telfer et al. 2002; Richards et al. 2003), the rest-frame UV luminosity of LAEs, and the sensitivity limits of these multi-wavelength data, we rule out the possibility that the LAEs have radio-loud AGNs. 4.4 UV-nebular line flux Here we investigate whether the rest-frame UV-nebular lines of N v λλ1238,1240, C iv λλ1548,1550, He ii λ1640, and O iii]λλ1661, 1666 are detected from the bright LAEs. First, we check the detectability of the N v emission line, which is a coarse indicator of AGN presence. The wavelengths of N v are covered by the FOCAS, LDSS3, and IMACS optical spectra for both of the z ≃ 6.6 and z ≃ 5.7 LAE samples. In order to estimate the flux limits, we sample the 1D spectra in ∼10 Å bins (comparable to the Lyα line FWHM) around the expected wavelengths of N v. We then obtain the flux limit by using the flux distribution over a ±50 Å range of the expected wavelengths of N v. We find that there are no N v emission lines for all the 21 bright LAEs. The 2 σ flux limits for the N v emission lines are listed in table 7. The line flux ratio of N v to Lyα is typically fNV/fLyα ≲ 10%. Table 7. UV-nebular emission lines of bright LAEs.* Object ID  Flux (EW0) (2 σ upper limits)  Line flux ratio relative to Lyα  (R.A.)  N v  C iv  He ii  O iii]  N v  C iv  He ii  O iii]      /Lyα  /Lyα  /Lyα  /Lyα    (10−17 erg s−1 cm−2) (Å)          (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  J162126  <0.81(<7.2)  <0.13(<1.8)  <0.35(<5.4)  <0.22(<3.5)  <0.05  <0.01  <0.02  <0.01  J233125  <0.53  —  —  —  <0.06  —  —  —  J160234  <0.71  <0.81  <1.06  <1.55  <0.11  <0.12  <0.16  <0.23  J160940  <0.56  <0.77  <1.20  <1.95  <0.14  <0.19  <0.30  <0.49  J100334  <0.75  —  —  —  <0.12  —  —  —  J100550  <0.64(<6.6)  <0.07(<1.1)  <0.05(0.91)  <0.16(<3.0)  <0.08  <0.01  <0.01  <0.03  J160707  <0.55  —  —  —  <0.09  —  —  —  J160107  <0.66  —  —  —  <0.27  —  —  —  J233408  <0.67  1.15(>42)  <0.16  <0.09  <0.05  0.08 ± 0.008  <0.01  <0.01  J021835  <0.92(<8.2)  <0.30(<4.2)  <0.39(<6.1)  <0.06(<1.0)  <0.07  <0.02  <0.03  <0.01  J233454  <0.64(<11)  <0.08(<2.1)  <0.12(<3.5)  <0.13(<3.9)  <0.05  <0.01  <0.01  <0.01  J201752  <0.70  —  —  —  <0.06  —  —  —  J021828  <0.62  —  —  —  <0.09  —  —  —  J021724  <0.15  —  —  —  <0.03  —  —  —  J021859  <0.59  —  —  —  <0.13  —  —  —  J021836  <0.26  —  —  —  <0.05  —  —  —  J232558  <0.45  —  —  —  <0.13  —  —  —  J022001  <0.72  —  —  —  <0.14  —  —  —  J021827  <1.05  —  —  —  <0.20  —  —  —  J021830  <1.24  —  —  —  <0.17  —  —  —  J021624  <0.43  —  —  —  <0.10  —  —  —  Object ID  Flux (EW0) (2 σ upper limits)  Line flux ratio relative to Lyα  (R.A.)  N v  C iv  He ii  O iii]  N v  C iv  He ii  O iii]      /Lyα  /Lyα  /Lyα  /Lyα    (10−17 erg s−1 cm−2) (Å)          (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  J162126  <0.81(<7.2)  <0.13(<1.8)  <0.35(<5.4)  <0.22(<3.5)  <0.05  <0.01  <0.02  <0.01  J233125  <0.53  —  —  —  <0.06  —  —  —  J160234  <0.71  <0.81  <1.06  <1.55  <0.11  <0.12  <0.16  <0.23  J160940  <0.56  <0.77  <1.20  <1.95  <0.14  <0.19  <0.30  <0.49  J100334  <0.75  —  —  —  <0.12  —  —  —  J100550  <0.64(<6.6)  <0.07(<1.1)  <0.05(0.91)  <0.16(<3.0)  <0.08  <0.01  <0.01  <0.03  J160707  <0.55  —  —  —  <0.09  —  —  —  J160107  <0.66  —  —  —  <0.27  —  —  —  J233408  <0.67  1.15(>42)  <0.16  <0.09  <0.05  0.08 ± 0.008  <0.01  <0.01  J021835  <0.92(<8.2)  <0.30(<4.2)  <0.39(<6.1)  <0.06(<1.0)  <0.07  <0.02  <0.03  <0.01  J233454  <0.64(<11)  <0.08(<2.1)  <0.12(<3.5)  <0.13(<3.9)  <0.05  <0.01  <0.01  <0.01  J201752  <0.70  —  —  —  <0.06  —  —  —  J021828  <0.62  —  —  —  <0.09  —  —  —  J021724  <0.15  —  —  —  <0.03  —  —  —  J021859  <0.59  —  —  —  <0.13  —  —  —  J021836  <0.26  —  —  —  <0.05  —  —  —  J232558  <0.45  —  —  —  <0.13  —  —  —  J022001  <0.72  —  —  —  <0.14  —  —  —  J021827  <1.05  —  —  —  <0.20  —  —  —  J021830  <1.24  —  —  —  <0.17  —  —  —  J021624  <0.43  —  —  —  <0.10  —  —  —  *(1) Object ID. (2)–(5) Flux and 2 σ flux upper limits of the C iv, He ii, and O iii] emission lines. The numbers in parentheses are the EW and 2 σ limits of the C iv, He ii, and O iii] emission lines. (6)–(9) Line flux ratios of the UV-nebular emission lines relative to Lyα. View Large Table 8. Spectroscopically confirmed z ≃ 6.6 LAEs with NB > 24 mag.* Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB921  y  Reference    (hms)  (° ΄ ″)    (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J021843−050915  02:18:43.62  −05:09:15.63  6.510  24.33  24.87  Hari  HSC J021703−045619  02:17:03.46  −04:56:19.07  6.589  24.45  25.42  O10  HSC J021827−043507  02:18:27.01  −04:35:07.92  6.511  24.56  25.32  O10  HSC J021844−043636  02:18:44.64  −04:36:36.21  6.621  24.63  27.34  H  HSC J021702−050604  02:17:02.56  −05:06:04.61  6.545  24.64  26.35  O10  HSC J021826−050726  02:18:27.00  −05:07:26.89  6.554  24.69  —  O10  HSC J021819−050900  02:18:19.39  −05:09:00.65  6.563  24.73  26.04  O10  HSC J021654−045556  02:16:54.54  −04:55:56.94  6.617  24.82  25.67  O10  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB921  y  Reference    (hms)  (° ΄ ″)    (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J021843−050915  02:18:43.62  −05:09:15.63  6.510  24.33  24.87  Hari  HSC J021703−045619  02:17:03.46  −04:56:19.07  6.589  24.45  25.42  O10  HSC J021827−043507  02:18:27.01  −04:35:07.92  6.511  24.56  25.32  O10  HSC J021844−043636  02:18:44.64  −04:36:36.21  6.621  24.63  27.34  H  HSC J021702−050604  02:17:02.56  −05:06:04.61  6.545  24.64  26.35  O10  HSC J021826−050726  02:18:27.00  −05:07:26.89  6.554  24.69  —  O10  HSC J021819−050900  02:18:19.39  −05:09:00.65  6.563  24.73  26.04  O10  HSC J021654−045556  02:16:54.54  −04:55:56.94  6.617  24.82  25.67  O10  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5)–(6) Total magnitudes of NB921 and y band. (7) Reference (O10: Ouchi et al. 2010; Hari: Y. Harikane in preparation; H: R. Higuchi in preparation). Note that the magnitudes are values directly obtained from the HSC catalog. View Large Table 9. Spectroscopically confirmed z ≃ 5.7 LAEs with NB > 24 mag. Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB816  z  Reference          (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB816 (z ≃ 5.7)  HSC J095952+013723  09:59:52.13  +01:37:23.24  5.724  24.07  25.76  M12  HSC J021758−043030  02:17:58.91  −04:30:30.42  5.689  24.07  25.56  H  HSC J095933+024955  09:59:33.44  +02:49:55.92  5.724  24.10  27.25  M12  HSC J021749−052854  02:17:49.11  −05:28:54.17  5.694  24.10  26.77  O08  HSC J021704−052714  02:17:04.30  −05:27:14.30  5.686  24.11  26.29  H  HSC J095952+015005  09:59:52.03  +01:50:05.95  5.744  24.11  25.10  M12  HSC J021737−043943  02:17:37.96  −04:39:43.02  5.755  24.11  25.63  H  HSC J100015+020056  10:00:15.66  +02:00:56.04  5.718  24.15  26.08  M12  HSC J021734−044558  02:17:34.57  −04:45:58.95  5.702  24.20  25.44  H  HSC J100131+023105  10:01:31.08  +02:31:05.77  5.690  24.23  26.15  M12  HSC J100301+020236  10:03:01.15  +02:02:36.04  5.682  24.24  24.58  M12  HSC J021654−052155  02:16:54.60  −05:21:55.52  5.712  24.24  26.49  H  HSC J021748−053127  02:17:48.46  −05:31:27.02  5.690  24.25  25.67  O08  HSC J100127+023005  10:01:27.77  +02:30:05.83  5.696  24.28  25.61  M12  HSC J021745−052936  02:17:45.24  −05:29:36.01  5.688  24.30  27.26  O08  HSC J021725−050737  02:17:25.90  −05:07:37.59  5.704  24.35  26.21  H  HSC J100208+015444  10:02:08.80  +01:54:44.99  5.676  24.36  25.65  M12  HSC J095954+021039  09:59:54.77  +02:10:39.26  5.662  24.38  25.63  M12  HSC J095950+025406  09:59:50.09  +02:54:06.16  5.726  24.39  26.59  M12  HSC J022013−045109  02:20:13.33  −04:51:09.40  5.744  24.40  25.88  O08  HSC J100126+014430  10:01:26.88  +01:44:30.29  5.686  24.41  25.96  M12  HSC J095919+020322  09:59:19.74  +02:03:22.02  5.704  24.41  26.84  M12  HSC J095954+021516  09:59:54.52  +02:15:16.50  5.688  24.43  25.95  M12  HSC J021849−052235  02:18:49.00  −05:22:35.35  5.719  24.45  25.64  H  HSC J100005+020717  10:00:05.06  +02:07:17.01  5.704  24.46  26.64  M12  HSC J021830−052950  02:18:30.75  −05:29:50.34  5.707  24.46  28.89  H  HSC J100306+014742  10:03:06.13  +01:47:42.69  5.680  24.52  26.54  M12  HSC J021804−052147  02:18:04.17  −05:21:47.25  5.734  24.54  25.20  H  HSC J100022+024103  10:00:22.51  +02:41:03.25  5.661  24.55  25.34  M12  HSC J021848−051715  02:18:48.23  −05:17:15.45  5.741  24.56  25.45  H  HSC J021750−050203  02:17:50.86  −05:02:03.24  5.708  24.57  26.48  H  HSC J021526−045229  02:15:26.22  −04:52:29.93  5.655  24.62  24.95  H  HSC J021636−044723  02:16:36.44  −04:47:23.68  5.718  24.63  26.57  H  HSC J100030+021714  10:00:30.41  +02:17:14.73  5.695  24.65  26.70  M12  HSC J021558−045301  02:15:58.49  −04:53:01.75  5.718  24.68  26.55  H  HSC J021719−043150  02:17:19.13  −04:31:50.64  5.735  24.68  27.87  H  HSC J021822−042925  02:18:22.91  −04:29:25.89  5.697  24.68  27.65  H  HSC J100131+014320  10:01:31.11  +01:43:20.50  5.728  24.70  26.45  M12  HSC J095944+020050  09:59:44.07  +02:00:50.74  5.688  24.71  26.18  M12  HSC J021709−050329  02:17:09.77  −05:03:29.18  5.709  24.74  26.52  H  HSC J021803−052643  02:18:03.87  −05:26:43.45  5.747  24.75  27.66  H  HSC J100309+015352  10:03:09.81  +01:53:52.36  5.705  24.76  26.61  M12  HSC J021805−052704  02:18:05.17  −05:27:04.06  5.746  24.77  31.43  H  HSC J021739−043837  02:17:39.25  −04:38:37.21  5.720  24.79  27.00  H  HSC J100040+021903  10:00:40.24  +02:19:03.70  5.719  24.81  26.96  M12  HSC J021857−045648  02:18:57.32  −04:56:48.88  5.681  24.85  27.11  H  HSC J021745−044129  02:17:45.74  −04:41:29.24  5.674  24.86  27.34  H  HSC J021639−051346  02:16:39.89  −05:13:46.75  5.702  24.87  26.98  H  HSC J021805−052026  02:18:05.28  −05:20:26.90  5.742  24.87  26.10  H  HSC J021755−043251  02:17:55.40  −04:32:51.54  5.691  24.91  27.26  H  HSC J100058+013642  10:00:58.41  +01:36:42.89  5.688  24.91  27.97  M12  HSC J100029+015000  10:00:29.58  +01:50:00.78  5.707  24.97  26.80  M12  HSC J021911−045707  02:19:11.03  −04:57:07.48  5.704  25.00  27.46  H  HSC J021551−045325  02:15:51.34  −04:53:25.44  5.710  25.02  26.76  H  HSC J021625−045237  02:16:25.64  −04:52:37.18  5.728  25.07  —  H  HSC J021751−053003  02:17:51.14  −05:30:03.64  5.712  25.10  26.99  O08  HSC J021628−050103  02:16:28.05  −05:01:03.85  5.692  25.17  27.23  H  HSC J021943−044914  02:19:43.91  −04:49:14.30  5.684  25.17  26.86  H  HSC J100029+024115  10:00:29.13  +02:41:15.70  5.735  25.22  28.30  M12  HSC J100107+015222  10:01:07.35  +01:52:22.88  5.668  25.33  26.42  M12  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB816  z  Reference          (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB816 (z ≃ 5.7)  HSC J095952+013723  09:59:52.13  +01:37:23.24  5.724  24.07  25.76  M12  HSC J021758−043030  02:17:58.91  −04:30:30.42  5.689  24.07  25.56  H  HSC J095933+024955  09:59:33.44  +02:49:55.92  5.724  24.10  27.25  M12  HSC J021749−052854  02:17:49.11  −05:28:54.17  5.694  24.10  26.77  O08  HSC J021704−052714  02:17:04.30  −05:27:14.30  5.686  24.11  26.29  H  HSC J095952+015005  09:59:52.03  +01:50:05.95  5.744  24.11  25.10  M12  HSC J021737−043943  02:17:37.96  −04:39:43.02  5.755  24.11  25.63  H  HSC J100015+020056  10:00:15.66  +02:00:56.04  5.718  24.15  26.08  M12  HSC J021734−044558  02:17:34.57  −04:45:58.95  5.702  24.20  25.44  H  HSC J100131+023105  10:01:31.08  +02:31:05.77  5.690  24.23  26.15  M12  HSC J100301+020236  10:03:01.15  +02:02:36.04  5.682  24.24  24.58  M12  HSC J021654−052155  02:16:54.60  −05:21:55.52  5.712  24.24  26.49  H  HSC J021748−053127  02:17:48.46  −05:31:27.02  5.690  24.25  25.67  O08  HSC J100127+023005  10:01:27.77  +02:30:05.83  5.696  24.28  25.61  M12  HSC J021745−052936  02:17:45.24  −05:29:36.01  5.688  24.30  27.26  O08  HSC J021725−050737  02:17:25.90  −05:07:37.59  5.704  24.35  26.21  H  HSC J100208+015444  10:02:08.80  +01:54:44.99  5.676  24.36  25.65  M12  HSC J095954+021039  09:59:54.77  +02:10:39.26  5.662  24.38  25.63  M12  HSC J095950+025406  09:59:50.09  +02:54:06.16  5.726  24.39  26.59  M12  HSC J022013−045109  02:20:13.33  −04:51:09.40  5.744  24.40  25.88  O08  HSC J100126+014430  10:01:26.88  +01:44:30.29  5.686  24.41  25.96  M12  HSC J095919+020322  09:59:19.74  +02:03:22.02  5.704  24.41  26.84  M12  HSC J095954+021516  09:59:54.52  +02:15:16.50  5.688  24.43  25.95  M12  HSC J021849−052235  02:18:49.00  −05:22:35.35  5.719  24.45  25.64  H  HSC J100005+020717  10:00:05.06  +02:07:17.01  5.704  24.46  26.64  M12  HSC J021830−052950  02:18:30.75  −05:29:50.34  5.707  24.46  28.89  H  HSC J100306+014742  10:03:06.13  +01:47:42.69  5.680  24.52  26.54  M12  HSC J021804−052147  02:18:04.17  −05:21:47.25  5.734  24.54  25.20  H  HSC J100022+024103  10:00:22.51  +02:41:03.25  5.661  24.55  25.34  M12  HSC J021848−051715  02:18:48.23  −05:17:15.45  5.741  24.56  25.45  H  HSC J021750−050203  02:17:50.86  −05:02:03.24  5.708  24.57  26.48  H  HSC J021526−045229  02:15:26.22  −04:52:29.93  5.655  24.62  24.95  H  HSC J021636−044723  02:16:36.44  −04:47:23.68  5.718  24.63  26.57  H  HSC J100030+021714  10:00:30.41  +02:17:14.73  5.695  24.65  26.70  M12  HSC J021558−045301  02:15:58.49  −04:53:01.75  5.718  24.68  26.55  H  HSC J021719−043150  02:17:19.13  −04:31:50.64  5.735  24.68  27.87  H  HSC J021822−042925  02:18:22.91  −04:29:25.89  5.697  24.68  27.65  H  HSC J100131+014320  10:01:31.11  +01:43:20.50  5.728  24.70  26.45  M12  HSC J095944+020050  09:59:44.07  +02:00:50.74  5.688  24.71  26.18  M12  HSC J021709−050329  02:17:09.77  −05:03:29.18  5.709  24.74  26.52  H  HSC J021803−052643  02:18:03.87  −05:26:43.45  5.747  24.75  27.66  H  HSC J100309+015352  10:03:09.81  +01:53:52.36  5.705  24.76  26.61  M12  HSC J021805−052704  02:18:05.17  −05:27:04.06  5.746  24.77  31.43  H  HSC J021739−043837  02:17:39.25  −04:38:37.21  5.720  24.79  27.00  H  HSC J100040+021903  10:00:40.24  +02:19:03.70  5.719  24.81  26.96  M12  HSC J021857−045648  02:18:57.32  −04:56:48.88  5.681  24.85  27.11  H  HSC J021745−044129  02:17:45.74  −04:41:29.24  5.674  24.86  27.34  H  HSC J021639−051346  02:16:39.89  −05:13:46.75  5.702  24.87  26.98  H  HSC J021805−052026  02:18:05.28  −05:20:26.90  5.742  24.87  26.10  H  HSC J021755−043251  02:17:55.40  −04:32:51.54  5.691  24.91  27.26  H  HSC J100058+013642  10:00:58.41  +01:36:42.89  5.688  24.91  27.97  M12  HSC J100029+015000  10:00:29.58  +01:50:00.78  5.707  24.97  26.80  M12  HSC J021911−045707  02:19:11.03  −04:57:07.48  5.704  25.00  27.46  H  HSC J021551−045325  02:15:51.34  −04:53:25.44  5.710  25.02  26.76  H  HSC J021625−045237  02:16:25.64  −04:52:37.18  5.728  25.07  —  H  HSC J021751−053003  02:17:51.14  −05:30:03.64  5.712  25.10  26.99  O08  HSC J021628−050103  02:16:28.05  −05:01:03.85  5.692  25.17  27.23  H  HSC J021943−044914  02:19:43.91  −04:49:14.30  5.684  25.17  26.86  H  HSC J100029+024115  10:00:29.13  +02:41:15.70  5.735  25.22  28.30  M12  HSC J100107+015222  10:01:07.35  +01:52:22.88  5.668  25.33  26.42  M12  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5)–(6) Total magnitudes of NB816 and z-bands. (7) Reference (M12: Mallery et al. 2012; O08: Ouchi et al. 2008; H: R. Higuchi in preparation). Note that the magnitudes are values directly obtained from the HSC catalog. View Large Next, we search for the UV-nebular emission lines of C iv, He ii, and O iii] for the seven bright LAEs whose NIR spectra were obtained (subsection 3.2). Figure 6 presents the NIR spectra for the seven LAEs. Even in the deep NIR spectra with a 3 σ line flux sensitivity limit of ∼2 × 10−18 erg s−1 cm−2, we find no significant emission features at the expected wavelengths of redshifted He ii, C iv, and O iii] lines, except for a tentative C iv detection from a z ≃ 5.7 LAE, HSC J233408+004403 (see below in this section). The flux limits for the C iv, He ii, and O iii] emission lines are estimated in the same manner as that for N v. To estimate the detection limits, we assume a single emission line even for the C iv and O iii] doublets which are resolved in the spectral resolution of MOSFIRE and nuMOIRCS. The 2 σ flux limits for individual UV-nebular emission lines are listed in table 7. Fig. 6. View largeDownload slide NIR spectra for the bright LAEs at z ≃ 6.6 (the upper four spectra) and ≃ 5.7 (the lower three spectra). The left figures are three-color composite images of the bright LAEs. The blue ticks denote the C iv (left), He ii (center), and O iii] (right) wavelengths which are expected from the redshift of Lyα emission lines. For HSC J162126+545719, the emission feature near the expected C iv λ1550 wavelength is likely to be a residual of the sky subtraction, which is marked by a black cross. A C iv λ1550 emission line is tentatively detected in the spectrum of HSC J233408+004403 (see figure 7), which is discussed in subsection 5.3. (Color online) Fig. 6. View largeDownload slide NIR spectra for the bright LAEs at z ≃ 6.6 (the upper four spectra) and ≃ 5.7 (the lower three spectra). The left figures are three-color composite images of the bright LAEs. The blue ticks denote the C iv (left), He ii (center), and O iii] (right) wavelengths which are expected from the redshift of Lyα emission lines. For HSC J162126+545719, the emission feature near the expected C iv λ1550 wavelength is likely to be a residual of the sky subtraction, which is marked by a black cross. A C iv λ1550 emission line is tentatively detected in the spectrum of HSC J233408+004403 (see figure 7), which is discussed in subsection 5.3. (Color online) Our deep NIR spectroscopy indicates that there are no significant detections of UV-nebular emission lines for bright LAEs. By visual inspection for the NIR spectra, we find a tentative detection of the C iv λ1550 emission line from the brightest LAE in the z ≃ 5.7 sample, HSC J233408+004403. Figure 7 shows the NIR spectra around the wavelengths of the C iv emission line doublet for HSC J233408+004403. The C iv λ1550 emission line is tentatively detected at the ∼4 σ–9 σ significance level. The significance of the line detection depends on the wavelength range of flux integration. We also identify two negative C iv λ1550 emission lines which could originate from the ±3″ slit dithering processes in the MOSFIRE observation. Moreover, the tentative C iv λ1550 detection might explain a possible magnitude excess in the y-band covering the C iv wavelength (see figure 3). The line flux is ∼1.2 × 10−17 erg cm−2 s−1. The emission line has a velocity width of ΔVFWHM ≃ 50 km s−1, which is marginally resolved in the MOSFIRE spectral resolution. We do not detect the C iv λ1548 component of the C iv doublet from HSC J233408+004403. The single C iv emission line at λrest ≃ 1550 Å may be formed by a combination of absorption and emission lines that could originate from stellar winds and ISM. Such a C iv line profile has been found for z ≃ 1–3 galaxies (e.g., Shapley et al. 2003; Erb et al. 2010; Du et al. 2016). We discuss the emission line properties of the C iv emitter in subsection 5.3. Fig. 7. View largeDownload slide Tentative detection of a C iv λ1550 emission line for HSC J233408+004403. The 2D spectra in the top and middle panels present the S/N and flux maps, respectively. The bottom panel shows the 1D spectrum of the flux map. The white arrows indicate the expected positions of the negative C iv λ1550 emission lines which are produced in the ±3″ slit dithering processes. The top-left panel depicts the 1D S/N spectrum along the spatial direction at the tentative C iv λ1550 emission line. The blue ticks and the red arrows indicate the C iv λ1548 and C iv λ1550 wavelengths expected from the Lyα emission line (i.e., zLyα = 5.707). The cyan dashed line shows the OH sky emission. The C iv λ1550 emission line is tentatively detected at a significance level of ∼4–9. (Color online) Fig. 7. View largeDownload slide Tentative detection of a C iv λ1550 emission line for HSC J233408+004403. The 2D spectra in the top and middle panels present the S/N and flux maps, respectively. The bottom panel shows the 1D spectrum of the flux map. The white arrows indicate the expected positions of the negative C iv λ1550 emission lines which are produced in the ±3″ slit dithering processes. The top-left panel depicts the 1D S/N spectrum along the spatial direction at the tentative C iv λ1550 emission line. The blue ticks and the red arrows indicate the C iv λ1548 and C iv λ1550 wavelengths expected from the Lyα emission line (i.e., zLyα = 5.707). The cyan dashed line shows the OH sky emission. The C iv λ1550 emission line is tentatively detected at a significance level of ∼4–9. (Color online) 4.5 Reanalysis of CR7 spectra We investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He ii is claimed by Sobral et al. (2015). Two of the authors in this paper and the ESO-archive service reanalyzed the VLT/X-SHOOTER data that were used in the study of Sobral et al. (2015). We applied three methods to our reanalysis: (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D). We smooth our reduced X-SHOOTER spectra with a kernel of ∼0.4 Å width, which corresponds to that of Sobral et al. (2015). Figure 8 presents our reduced X-SHOOTER data for the optical (the left panel) and NIR (the right panel) arms for CR7 with the 1D spectrum obtained by Sobral et al. (2015). As shown in the left panel of figure 8, we clearly identify a Lyα emission line at λrest = 1216 Å. The Lyα line profiles of our data are in good agreement with that of the Sobral et al.’s optical spectrum. However, we find no signal at λrest = 1640 Å, where Sobral et al. (2015) find the emission line feature (the right panel of figure 8). The detection significance is <1 σ at λrest = 1640 Å in our NIR spectra. Instead, our NIR spectra show a feature of two possible peaks at λrest = 1643 Å, which is redder than the He ii wavelength of Sobral et al. (2015) by Δλrest ≃ 3 Å, corresponding to the redshift difference of Δz = 0.01. If we regard the two possible peaks as He ii, we obtain a detection significance of ∼1.8 σ. This significance value is inconsistent with the 6 σ detection of Sobral et al. (2015). Moreover, the red component of the two possible peaks appears to be made by sky subtraction residuals, as shown in figure 8a. In the case that this red component is masked for the line flux calculation, the detection significance decreases to ∼1.1 σ. To obtain all the values of detection significance and noise levels, we use OH sky line-free regions. Fig. 8. View largeDownload slide Reanalyzed VLT/X-SHOOTER spectra of CR7. The left and right panels denote the VIS and NIR arms of the X-SHOOTER spectra. The blue lines indicate the X-SHOOTER spectra in Sobral et al. (2015). The red, magenta, and orange lines depict spectra obtained from (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D), respectively. These lines have been smoothed with a kernel of ∼0.4 Å width, which is similar to that of Sobral et al. (2015). The gray lines present the unsmoothed spectrum obtained from our data reduction with ESO REFLEX. The thin blue and red lines indicate sky OH lines in Sobral et al. (2015) and our reanalyzed data, respectively. The top-left panels show the 2D spectrum of the X-SHOOTER VIS arm. The top-right panels indicate (a) sky OH line, (b) unsmoothed, and (c) smoothed 2D spectra, all of which are obtained from our data reduction with ESO REFLEX. The feature at λrest = 1643 Å appears to be made by sky subtraction residuals. The blue ticks indicate the position of He ii, whose detection is claimed by Sobral et al. (2015). See subsection 4.5 for more details. (Color online) Fig. 8. View largeDownload slide Reanalyzed VLT/X-SHOOTER spectra of CR7. The left and right panels denote the VIS and NIR arms of the X-SHOOTER spectra. The blue lines indicate the X-SHOOTER spectra in Sobral et al. (2015). The red, magenta, and orange lines depict spectra obtained from (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D), respectively. These lines have been smoothed with a kernel of ∼0.4 Å width, which is similar to that of Sobral et al. (2015). The gray lines present the unsmoothed spectrum obtained from our data reduction with ESO REFLEX. The thin blue and red lines indicate sky OH lines in Sobral et al. (2015) and our reanalyzed data, respectively. The top-left panels show the 2D spectrum of the X-SHOOTER VIS arm. The top-right panels indicate (a) sky OH line, (b) unsmoothed, and (c) smoothed 2D spectra, all of which are obtained from our data reduction with ESO REFLEX. The feature at λrest = 1643 Å appears to be made by sky subtraction residuals. The blue ticks indicate the position of He ii, whose detection is claimed by Sobral et al. (2015). See subsection 4.5 for more details. (Color online) In our careful reanalysis for the X-SHOOTER data, we find that no He ii signal of CR7 is detected. This supports weak UV-nebular lines of the bright LAEs even for CR7. Based on our S/N-based reanalysis and the flux error from Sobral et al. (2015), we obtain 3 σ upper limits of He ii flux and EW for CR7, $$f_{\rm He\,{\scriptscriptstyle II}}<2.1\times 10^{-17}\:$$erg s−1 cm−2 and $$EW_{\rm He\,{\scriptscriptstyle II}}< 60$$ Å, respectively.4 4.6 Line flux ratios Figure 9 presents the line flux ratios of He ii/Lyα and C iv/Lyα for our bright LAEs and several Lyα-emitting populations such as z ≃ 6–7 LAEs (Nagao et al. 2005; Kashikawa et al. 2012; Zabl et al. 2015), spatially extended Lyα blobs (LABs: Dey et al. 2005; Prescott et al. 2009, 2013; Arrigoni Battaia et al. 2015), z ≃ 2–3 metal-poor and star-forming galaxies (Shapley et al. 2003; Erb et al. 2010), AGNs, QSOs, and radio galaxies (Heckman et al. 1991; Villar-Martín et al. 2007; Humphrey et al. 2013; Borisova et al. 2016).5 We add CR7 with our updated He ii/Lyα constraint in subsection 4.5. The UV-nebular lines of C iv, He ii, and O iii] are not detected from all of our seven bright LAEs, even for CR7, except for a tentative C iv detection (subsection 5.3). Albeit with only upper limits on the line flux ratios, we find that our bright LAEs typically have flux ratios of He ii/Lyα and C iv/Lyα lower than those of AGNs, QSOs, radio galaxies, and LABs, but similar to those of star-forming galaxies in Shapley et al. (2003) and Erb et al. (2010). Interestingly, the UV-nebular lines are extremely faint for several of our bright LAEs. For such objects, the flux ratio of the UV-nebular lines relative to Lyα, i.e., fUV line/fLyα, is below the order of 1%. Fig. 9. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/Lyα vs. C iv/Lyα. The red filled squares indicate our bright LAEs. The red cross denotes our bright LAE whose C iv emission line is tentatively detected (see subsection 5.3). The red open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The green arrow and dashed line are our He ii/Lyα constraint for CR7 (see subsection 4.5). The green filled symbols represent LABs (green filled square: Dey et al. 2005; green filled pentagons: Prescott et al. 2009, 2013; green filled diamonds: Arrigoni Battaia et al. 2015). The cyan filled symbols represent z ≃ 2–3 star-forming galaxies (cyan filled inverse triangle: Shapley et al. 2003; cyan filled circle Erb et al. 2010). The black and yellow symbols indicate AGNs, QSOs, and radio galaxies (black crosses: Villar-Martín et al. 2007; black filled triangles: Heckman et al. 1991; yellow filled triangles: Humphrey et al. 2013; black filled circles: Borisova et al. 2016). The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 9. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/Lyα vs. C iv/Lyα. The red filled squares indicate our bright LAEs. The red cross denotes our bright LAE whose C iv emission line is tentatively detected (see subsection 5.3). The red open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The green arrow and dashed line are our He ii/Lyα constraint for CR7 (see subsection 4.5). The green filled symbols represent LABs (green filled square: Dey et al. 2005; green filled pentagons: Prescott et al. 2009, 2013; green filled diamonds: Arrigoni Battaia et al. 2015). The cyan filled symbols represent z ≃ 2–3 star-forming galaxies (cyan filled inverse triangle: Shapley et al. 2003; cyan filled circle Erb et al. 2010). The black and yellow symbols indicate AGNs, QSOs, and radio galaxies (black crosses: Villar-Martín et al. 2007; black filled triangles: Heckman et al. 1991; yellow filled triangles: Humphrey et al. 2013; black filled circles: Borisova et al. 2016). The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) 5 Discussion 5.1 Properties of bright LAEs at z ≃ 6 We summarize the properties of the bright z ≃ 6–7 LAEs which have been revealed in our statistical study (section 4): The Lyα equivalent widths, EW0,Lyα, range from ∼10 Å to ∼300 Å. The Lyα line widths are ∼200–400 km s−1. There are no detections of X-ray, MIR, or radio emission. The N v emission line is not detected down to an N v/Lyα flux ratio of ∼10%. Most of the bright LAEs have compact Lyα emission. Only 5 objects out of the 28 bright LAEs show Lyα emission that is significantly extended compared to the point spread function FWHM size of ∼ 0$${^{\prime\prime}_{.}}$$7 in the ground-based HSC NB images. The UV-nebular lines of C iv, He ii, and O iii] are not detected from any of our seven bright LAEs, even for CR7, except for a tentative C iv detection (subsection 5.3). The flux ratio of the UV-nebular lines relative to Lyα is fUV line/fLyα ≲ 1%–10%. Here we discuss the physical origins of bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The bright Lyα emission could be reproduced by several mechanisms: (1) gas photoionization by a hidden AGN, (2) strong UV radiation from Pop III stellar populations, (3) gas shock heating by strong outflows from central galaxies, and (4) intense starbursts by galaxy mergers. First, we discuss the possibility of AGNs. For z ≃ 2, Konno et al. (2016) have identified a significant excess of LAE number density at the Lyα LF bright end of log LLyα/[erg s−1] ≳ 43.4. All of the z ≃ 2 LAEs in the bright-end excess are detected in X-ray, UV, or radio data, suggesting that the bright Lyα emission is produced by central AGN activity. Similarly, there is a possibility that AGNs enhance the Lyα luminosity for bright LAEs at z ≃ 6–7. However, we find no clear signatures of AGNs according to the narrow Lyα line widths of ≲400 km s−1, and no detections of the N v line, X-ray, MIR, or radio emission. Thus, the bright LAEs at z ≃ 5.7–6.6 do not host broad-line AGNs, regardless of the bright Lyα emission. Secondly, we discuss the possibility of Pop III stellar populations. There is a possibility that strong UV radiation from Pop III stellar populations enhance the Lyα luminosity (e.g., Schaerer 2002). In our deep NIR spectroscopy, we find that there are no detections of the He ii emission line from CR7, Himiko, or our seven bright LAEs which are observed with NIR spectrographs. Moreover, the Lyα EW does not significantly exceed the EW0,Lyα value of 240 Å for the bright LAEs. No He ii detection and the small EW0,Lyα values might indicate that the bright LAEs do not host Pop III stellar populations. No Pop III stellar populations in bright LAEs might be supported by theoretical studies. According to a recent theoretical study of Yajima and Khochfar (2017), Pop III-dominated galaxies at z ≃ 7 have a Lyα luminosity of LLyα ≃ 3.0 × 1042–2.1 × 1043 erg s−1, which is slightly lower than that of our bright LAEs. However, we cannot reach the conclusion that Pop III stellar populations exist in bright LAEs from the current data of He ii measurements. The detectability of the He ii emission line would largely depend on the stellar initial mass function of galaxies (see subsection 5.4). To examine whether bright LAEs host Pop III stellar populations, we require NIR spectra whose depth is ∼10 × deeper than the current NIR flux limits. Thirdly, we discuss the possibility that strong outflows enhance the Lyα luminosity (e.g., Dijkstra & Wyithe 2010). If strong outflows exist, expelling high-velocity clouds could make Lyα lines broad and Lyα emission spatially extended. Our spectroscopy reveals that bright LAEs have a narrow Lyα emission line of ΔVFWHM ≲ 400 km s−1. Our Aiso measurements also indicate that most of our bright LAEs show spatially compact Lyα emission (see subsection 4.1 and table 6). The narrow Lyα line width and the spatially compact Lyα emission might suggest no strong gaseous outflow from the bright LAEs. However, we cannot conclude the presence of gaseous outflow based on our current data of optical spectra and NB images due to the resonance nature of Lyα photons. To investigate the presence of gaseous outflow, we have to directly measure velocity shifts of low-ionization metal lines with deep NIR spectra for the rest-frame UV continuum emission (e.g., Shibuya et al. 2014a; Erb et al. 2014, 2015; Trainor et al. 2015; Sugahara et al. 2017). Finally, we discuss the possibility that intense starbursts driven by galaxy mergers produce the large Lyα luminosity. High spatial resolution imaging observations with Hubble WFC3 have been conducted for two objects out of the 28 bright LAEs, Himiko and CR7, both of which show multiple subcomponents in the rest-frame UV continuum emission (Ouchi et al. 2013; Sobral et al. 2015). These multiple subcomponents could be indicative of galaxy mergers (e.g., Jiang et al. 2013; Shibuya et al. 2014b; Kobayashi et al. 2016). However, the galaxy morphology has been unclear for the other 26 bright LAEs in the ground-based and seeing-limited HSC images. In summary, the physical origins of bright LAEs are still unknown. At least we can conclude that the bright Lyα emission does not originate from broad-line AGNs. To obtain a definitive conclusion, we need to systematically perform deep NIR spectroscopy and high spatial resolution imaging observations for a large number of bright LAEs. 5.2 Relation between UV-nebular line EW and UV-continuum luminosity Combining samples of our bright LAEs and faint dropouts at z ≃ 5–7, we examine the relation between the UV-nebular line EWs of C iv, He ii, and O iii] and UV-continuum luminosity. Figure 10 presents the rest-frame EW of C iv, He ii, and O iii] as a function of MUV for our bright LAEs and dropouts in the literature (e.g., Stark et al. 2015; Mainali et al. 2017; Smit et al. 2017). Here we plot four UV continuum-detected objects out of our seven bright LAEs whose UV-nebular line EW can be constrained. The EW upper limits of our bright LAEs are typically ≲2.3, 4.0, and 2.9 Å for C iv, He ii, and O iii] lines, respectively. On the other hand, faint dropouts with MUV ≳ −20 strongly emit C iv and O iii] lines with $$EW_{\rm 0,C\,{\scriptscriptstyle IV}}\simeq 20$$–40 Å and $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}\simeq 5$$–10 Å, respectively. Fig. 10. View largeDownload slide Line equivalent widths of C iv (top), He ii (middle), and O iii] (bottom) as a function of UV magnitude, MUV. The red filled squares denote our four bright LAEs with an upper limit of UV-nebular line EW. The red cross represents the LAEs whose C iv emission is tentatively detected. The cyan filled symbols denote high-z dropout galaxies (cyan filled circles: z ≃ 7 dropouts in Stark et al. 2015; cyan filled diamond: z ≃ 6 dropout in Mainali et al. 2017; cyan filled triangle: Smit et al. 2017). The gray symbols indicate z ≃ 2–3 galaxies (gray crosses: Amorín et al. 2017; gray open inverse-triangle: Stark et al. 2014). The gray curves represent the best-fit quadratic functions to the data points of z ≃ 6–7 dropouts in Stark et al. 2014, Mainali et al. (2017), and our LAEs. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 10. View largeDownload slide Line equivalent widths of C iv (top), He ii (middle), and O iii] (bottom) as a function of UV magnitude, MUV. The red filled squares denote our four bright LAEs with an upper limit of UV-nebular line EW. The red cross represents the LAEs whose C iv emission is tentatively detected. The cyan filled symbols denote high-z dropout galaxies (cyan filled circles: z ≃ 7 dropouts in Stark et al. 2015; cyan filled diamond: z ≃ 6 dropout in Mainali et al. 2017; cyan filled triangle: Smit et al. 2017). The gray symbols indicate z ≃ 2–3 galaxies (gray crosses: Amorín et al. 2017; gray open inverse-triangle: Stark et al. 2014). The gray curves represent the best-fit quadratic functions to the data points of z ≃ 6–7 dropouts in Stark et al. 2014, Mainali et al. (2017), and our LAEs. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) As shown in figure 10, we find a trend that EWs of C iv and O iii] increase towards faint MUV. Such a trend is similar to recent study results for z ≃ 2–3 galaxies showing that UV-nebular lines are predominantly detected in faint sources (Stark et al. 2014; Amorín et al. 2017; see also Du et al. 2017 for C iii]λλ1907,1909). On the other hand, we do not find a clear trend for He ii due to no He ii detection from all of our bright LAEs or z ≃ 6–7 dropouts. For the clarity of the $$EW_{\rm 0,C\,{\scriptscriptstyle IV}}$$ and $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}$$ relations, we fit a quadratic function to the data points of z ≃ 6–7 dropouts in Stark et al. (2015), Mainali et al. (2017), and our LAEs. In the fit, we use the values of EW upper limits for the objects without a UV-nebular line detection. We exclude the LAE with a tentative C iv detection and a z ≃ 7 dropout with a weak $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}$$ constraint in Stark et al. (2015) for the fit (see subsection 5.3). The best-fit quadratic functions are shown in figure 10. In contrast to the gravitationally lensed and faint dropouts of Stark et al. (2015), Mainali et al. (2017), and Smit et al. (2017), our bright LAEs have a moderately bright UV magnitude ranging from MUV ≃ −20 to ≃ −22. No UV-nebular line detections from the bright sources could suggest that such a high EW0 value is a characteristic of low-mass galaxies. The high UV-nebular line EW in low-mass galaxies would be due to a hard ionizing spectrum (i.e., ξion, the number of LyC photons per UV luminosity; e.g., Nakajima et al. 2016; Bouwens et al. 2016). Moreover, recent studies for z ≃ 0 galaxies report that high-ionization UV-nebular lines highly depend on the gas-phase metallicity (e.g., Senchyna et al. 2017). Our possible EW–MUV correlation may also suggest a dependence of the UV-nebular line EW on metallicity for z ≃ 6–7 galaxies via the mass–metallicity relation. 5.3 A tentative detection of the C iv emission line In this section, we discuss the EW and UV-nebular line ratios for the LAE whose C iv is tentatively detected (subsection 4.4). We estimate the C iv EW, $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$, by using the upper limits of the rest-frame UV continuum flux density. We obtain $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}\gtrsim 40$$ Å, which is comparable to that of a z ≃ 7 dropout in Stark et al. (2015). The $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$ value might be too high according to the anti-correlation between EW and UV-continuum luminosity in subsection 5.2. However, it should be noted that the UV continuum is not detected for HSC J233408+004403. In the case that the UV magnitude is fainter than MUV ≃ −21, the $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$ value would be comparable to the trend that EW0 is high at a high UV-continuum luminosity. Assuming that the C iv emission line is detected in HSC J233408+004403, we compare the He ii/C iv and O iii]/C iv line flux ratios of HSC J233408+004403 with those of star-forming galaxies at z ≃ 0–7 and AGNs/QSOs (Hainline et al. 2011; Alexandroff et al. 2013; Stark et al. 2014; Berg et al. 2016; Vanzella et al. 2016, 2017; Mainali et al. 2017). Figure 11 shows the line flux ratios of He ii/C iv and O iii]/C iv for HSC J233408+004403 and star-forming galaxies and AGNs/QSOs. As shown in figure 11, HSC J233408+004403 has a flux ratio limit of log(He ii/C iv) ≲ −0.9, similar to that of star-forming galaxies at z ≃ 7. Fig. 11. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/C iv vs. O iii]/C iv. The red cross denotes our bright LAE with a tentative C iv emission, HSC J233408+004403. The cyan filled symbols indicate dropouts at z ≃ 2–7 (cyan squares: Vanzella et al. 2017; cyan filled inverse-triangle: Vanzella et al. 2016; cyan filled diamond: Mainali et al. 2017; cyan filled triangle: Stark et al. 2014). The green asterisks represent z ≃ 0 galaxies in Berg et al. (2016). The crosses represent QSOs and AGNs (black crosses: z ≃ 2–4 type-II QSOs in Alexandroff et al. 2013; magenta cross: z ≃ 2–3 AGN composite in Hainline et al. 2011). The blue and red arrows indicate the star-forming galaxy and AGN regions predicted by a photoionization model of Feltre, Charlot, and Gutkin (2016), respectively. (Color online) Fig. 11. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/C iv vs. O iii]/C iv. The red cross denotes our bright LAE with a tentative C iv emission, HSC J233408+004403. The cyan filled symbols indicate dropouts at z ≃ 2–7 (cyan squares: Vanzella et al. 2017; cyan filled inverse-triangle: Vanzella et al. 2016; cyan filled diamond: Mainali et al. 2017; cyan filled triangle: Stark et al. 2014). The green asterisks represent z ≃ 0 galaxies in Berg et al. (2016). The crosses represent QSOs and AGNs (black crosses: z ≃ 2–4 type-II QSOs in Alexandroff et al. 2013; magenta cross: z ≃ 2–3 AGN composite in Hainline et al. 2011). The blue and red arrows indicate the star-forming galaxy and AGN regions predicted by a photoionization model of Feltre, Charlot, and Gutkin (2016), respectively. (Color online) We compare the limits of flux ratios with those of photoionization models of star-forming galaxies and AGNs in Feltre, Charlot, and Gutkin (2016). The comparison suggests that the constraints on the line flux ratios for HSC J233408+004403 are more comparable to star-forming galaxies as ionizing sources than AGNs predicted by the model, supporting the results of no clear signatures of AGN activity in subsections 4.2 and 4.3. 5.4 Spectral hardness of bright LAEs We investigate the spectral hardness of bright LAEs at z ≃ 6–7 based on the upper limits on the He ii/Lyα line flux ratios (subsection 4.4). Figure 12 shows the spectral hardness, QHe +/QH, as a function of metallicity, Z, for our bright LAEs and z ≃ 6–7 LAEs in previous studies (Himiko in Zabl et al. 2015; SDF-LEW-1 in Kashikawa et al. 2012; SDF J132440.6+273607 in Nagao et al. 2005). Here we use QHe +/QH, which is more model independent than physical quantities of, e.g., ξion. The QHe +/QH value is calculated with   \begin{equation} \frac{f_{\rm He}}{f_{\rm Ly\alpha }} \simeq 0.55 \times \frac{Q({\rm He}^+)}{Q({\rm H})}, \end{equation} (1)where fHe and fLyα are the flux of the He ii and Lyα emission lines, respectively, and Q(He+) and Q(H) are the emitted number of hydrogen and helium ionizing photons, respectively. QHe +/QH traces the energy range between 54.4 and 13.6 eV. The factor of 0.55 depends on the electron temperature, here taken to be Te = 30 kK (Schaerer 2002). The Q(He+)/Q(H) upper limits calculated from the He ii/Lyα line flux ratios (table 7) ranges from log Q(He+)/Q(H) ≃ −0.5 to ∼−1.8. For five objects of our bright LAEs, we put strong upper limits of log Q(He+)/Q(H) ≲ −1.8. Fig. 12. View largeDownload slide Spectral hardness of the He+ ionizing flux, $$Q_{\rm He^+}/Q_{\rm H}$$, as a function of metallicity. The red filled circles represent our bright LAEs. The magenta line indicates the strongest upper limit of our $$Q_{\rm He^+}/Q_{\rm H}$$ estimates. The filled red squares, blue circles, and green triangles with colored lines denote the model predictions of Schaerer (2003) for stellar initial mass functions with mass ranges of 1–100 M⊙ , 1–500 M⊙ , and 50–500 M⊙ , respectively. The open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The open green pentagon is $$Q_{\rm He^+}/Q_{\rm H}$$ obtained from our He ii/Lyα constraint for CR7 (see subsection 4.5). The metallicity of the observational data points is arbitrary. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 12. View largeDownload slide Spectral hardness of the He+ ionizing flux, $$Q_{\rm He^+}/Q_{\rm H}$$, as a function of metallicity. The red filled circles represent our bright LAEs. The magenta line indicates the strongest upper limit of our $$Q_{\rm He^+}/Q_{\rm H}$$ estimates. The filled red squares, blue circles, and green triangles with colored lines denote the model predictions of Schaerer (2003) for stellar initial mass functions with mass ranges of 1–100 M⊙ , 1–500 M⊙ , and 50–500 M⊙ , respectively. The open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The open green pentagon is $$Q_{\rm He^+}/Q_{\rm H}$$ obtained from our He ii/Lyα constraint for CR7 (see subsection 4.5). The metallicity of the observational data points is arbitrary. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Figure 12 also shows the model spectral hardness predicted from initial mass functions (IMFs) with different stellar mass ranges of M* = 1–100 M⊙ , 1–500 M⊙ , and M* = 50–500 M⊙ (Schaerer 2003). The metallicity of bright LAEs has not been constrained yet. If we assume that bright LAEs are extremely metal poor below log Z ≃ −8, top-heavy IMFs with M* = 50–500 M⊙ might be ruled out by our QHe +/QH constraints for z ≃ 6–7 LAEs. 6 Summary and conclusions We present Lyα and UV-nebular emission line properties of bright LAEs at z = 6–7 with a luminosity of log LLyα/[erg s−1] = 43–44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru/HSC survey data (Ouchi et al. 2018; Shibuya et al. 2018). Our findings are summarized as follows: Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 97 LAEs at z = 6–7 in SILVERRUSH. Our observations enlarge a spectroscopic sample of bright LAEs by a factor of four, allowing for a statistical study on bright LAEs. We find that all the bright LAEs have a narrow Lyα line width of ≲400 km s−1, and do not have X-ray, MIR, radio, or N v λλ1238,1240 emissions regardless of the large Lyα luminosity. The narrow Lyα line widths and no X-ray, MIR, radio, or N v detections suggest that the bright LAEs are not broad-line AGNs. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS NIR spectroscopy, reaching the 3 σ flux limit of ∼2 × 10−18 erg s−1 for the UV-nebular emission lines of He ii λ1640, C iv λλ1548,1550, and O iii]λλ1661,1666. Except for one tentative detection of C iv, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of EW0 of ∼2.3, 4.0, and 2.9 Å for He ii, C iv, and O iii] lines, respectively. We investigate the VLT/X-SHOOTER spectrum of CR7, for which 6 σ detection of He ii is claimed by Sobral et al. (2015). Although two of the authors of this paper and the ESO-archive service carefully reanalyzed the X-SHOOTER data used in the study of Sobral et al. (2015), no He ii signal for CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. Spectral properties of these bright LAEs are clearly different from those of faint dropouts at z ∼ 7 that have strong UV-nebular lines, as shown in the various studies (e.g., Stark et al. 2015). Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and UV-continuum luminosity, which are similar to those found at z ≃ 2–3. The high spatial resolution imaging and deep spectroscopic observations with the Hubble Space Telescope and James Webb Space Telescope will reveal the morphology, ISM properties, and the origins of bright LAEs. Acknowledgements We would like to thank Masayuki Akiyama, Mark Dijkstra, Richard Ellis, Tadayuki Kodama, Jorryt Matthee, David Sobral, Daniel Stark, Yuma Sugahara, and Zheng Zheng for useful discussion and comments. We also thank Kentaro Aoki and Ichi Tanaka for their support of the FOCAS and MOIRCS observations. We thank the anonymous referee for constructive comments and suggestions. This work is based on observations taken by the Subaru Telescope and the Keck telescope, which are operated by the National Observatory of Japan. This work was supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, KAKENHI (15H02064), (23244025), and (21244013) Grant-in-Aid for Scientific Research (A) through Japan Society for the Promotion of Science (JSPS), and an Advanced Leading Graduate Course for Photon Science grant. NK is supported by JSPS grant 15H03645. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), the Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at ⟨http://dm.lsst.org⟩. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. Appendix. Spectroscopically confirmed LAEs with NB > 24 Tables 8 and 9 present faint NB > 24 spectroscopically confirmed HSC LAEs at z ≃ 6.6 and z ≃ 5.7, respectively. See sub-subsection 3.1.4 for more details. Footnotes † Based on data obtained with the Subaru Telescope. The Subaru Telescope is operated by the National Astronomical Observatory of Japan. ‡ This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. 1 ⟨http://cos.icrr.u-tokyo.ac.jp/rush.html⟩. 2 ⟨http://iraf.noao.edu/⟩. 3 ⟨https://keck-datareductionpipelines.github.io/MosfireDRP/⟩. 4 Recently, the He ii/Lyα line flux ratio for CR7 has been updated based on the flux recalibration of the X-SHOOTER spectrum in Matthee et al. (2017) and D. Sobral (in preparation). 5 Note that the C iv doublet is not spectroscopically resolved for some of the previous studies. The flux upper limit for such an unresolved C iv doublet would be higher than that of resolved C iv lines. 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Abstract

Abstract We present Lyα and UV-nebular emission line properties of bright Lyα emitters (LAEs) at z = 6–7 with a luminosity of log LLyα/[erg s−1] = 43–44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam survey data. Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 96 LAEs at z = 6–7 in SILVERRUSH. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3 σ flux limit of ∼2 × 10−18 erg s−1 for the UV-nebular emission lines of He ii λ1640, C iv λλ1548,1550, and O iii]λλ1661,1666. Except for one tentative detection of C iv, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW0) of ∼2–4 Å for C iv, He ii, and O iii] lines. We also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He ii is claimed by Sobral et al. Although two individuals and the ESO archive service carefully reanalyzed the X-SHOOTER data that are used in the study of Sobral et al., no He ii signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. The spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z ∼ 7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and the UV-continuum luminosity, which are similar to those found at z ∼ 2–3. 1 Introduction Bright Lyα-emitting galaxies are important objects in the studies of the early Universe and galaxy formation. Bright Lyα emission with log LLyα/[erg s−1] ≃ 43–44 is expected to be reproduced in various physical mechanisms (e.g., Fisher et al. 2014; Pallottini et al. 2015). Very young and metal-free stars (Population III, hereafter Pop III) hosted in galaxies would emit substantially strong Lyα radiation with a narrow He ii λ1640 line (≲200 km s−1) and a Lyα equivalent width (EW) enhancement. On the other hand, active galactic nuclei (AGNs) would also produce the bright Lyα emission with high ionization metal lines such as N v λλ1238,1240 and C iv λλ1548,1550 due to the strong UV radiation from the central ionizing source. In addition, the highly complex Lyα radiative transfer in the interstellar medium (ISM) makes it difficult to understand the Lyα emitting mechanism (e.g., Neufeld 1991; Hansen & Oh 2006). Lyα emitters (LAEs) have been surveyed by imaging observations with dedicated narrowband (NB) filters. During recent decades, the wide field of view (FoV) of Subaru/Suprime-Cam (SCam) has allowed us to identify LAE candidates at the bright end of Lyα luminosity functions (LFs; e.g., Taniguchi et al. 2005; Kashikawa et al. 2006, 2011; Shimasaku et al. 2006; Murayama et al. 2007; Ota et al. 2008; Ouchi et al. 2008, 2010; Hu et al. 2010; Konno et al. 2014; Matthee et al. 2015). Follow-up optical spectroscopic observations have confirmed several bright LAEs at z ≃ 6.6 (e.g., Himiko: Ouchi et al. 2009; CR7 and MASOSA: Sobral et al. 2015; COLA1: Hu et al. 2016; Bagley et al. 2017), and at z ≃ 5.7 (Mallery et al. 2012). However, subsequent multi-band observations have found heterogeneity in the nature of these bright LAEs. Zabl et al. (2015) have reported no detections of He ii or C iv from Himiko with VLT/X-SHOOTER. A deep ALMA observation reveals that Himiko has no strong [C ii]158 μm line and dust continuum emission (Ouchi et al. 2013). Combined with morphological properties, the bright Lyα emission of Himiko is probably caused by intense star formation in a galaxy merger. On the other hand, Sobral et al. (2015) have claimed that a narrow He ii line was detected at the 6 σ significance level from CR7 based on deep VLT/X-SHOOTER near-infrared (NIR) spectroscopy. The He ii detection might suggest that CR7 hosts Pop III stellar populations. Recently, a number of theoretical studies have discussed the strong He ii emission from CR7 (e.g., Pallottini et al. 2015; Agarwal et al. 2016; Hartwig et al. 2016; Dijkstra et al. 2016; Smidt et al. 2016; Smith et al. 2016; Visbal et al. 2016, 2017; Johnson & Dijkstra 2017; Pacucci et al. 2017). In contrast to the claim of He ii detection, CR7 clearly includes an old stellar population found from analyses of photometric data (Bowler et al. 2017), suggesting that this system is not be truly young. These studies indicate that the nature of bright LAEs has become a hot topic of debate. Even with these substantial observational and theoretical efforts, the diversity of bright LAEs has not yet been unveiled due to the limited statistics. In this paper, we present the results of our optical and NIR spectroscopic observations of bright LAEs selected with data from a new wide-FoV camera, Hyper Suprime-Cam (HSC), on the Subaru Telescope. In our spectroscopic observations, we newly identify 21 bright LAEs with log LLyα/[erg s−1] ≃ 43–44, which have enlarged the spectroscopic sample of bright LAEs by a factor of four. This is the third paper in our ongoing HSC research project for Lyα-emitting objects, Systematic Identification of LAEs for Visible Exploration and Reionization Research Using Subaru HSC (SILVERRUSH). In this project, we study various properties of high-z LAEs, e.g., LAE clustering (Ouchi et al. 2018), photometric properties of Lyα line EW and Lyα spatial extent (Shibuya et al. 2018), spectroscopic properties of bright LAEs (this study), Lyα LFs (Konno et al. 2018), and LAE overdensity (R. Higuchi et al. in preparation). This program is one of twin programs, the other being the study of dropouts, Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH: Toshikawa et al. 2018), detailed in Ono et al. (2018) and Harikane et al. (2018). Source catalogs for the LAEs and dropouts will be presented on our project webpage.1 This paper has the following structure. In section 2, we describe the HSC data and target selections of bright LAEs for our optical and NIR spectroscopy. Section 3 presents details of the spectroscopic observations for the bright LAEs and the data reduction. In section 4, we investigate physical properties of bright LAEs at z ≃ 6 using our statistical sample of bright LAEs. In section 5, we discuss the implications for galaxy formation and evolution. We summarize our findings in section 6. Throughout this paper, we adopt the concordance cosmology with (Ωm, ΩΛ, h) = (0.3, 0.7, 0.7) (Planck Collaboration 2016). All magnitudes are given in the AB system (Oke & Gunn 1983). 2 Targets for spectroscopy 2.1 Imaging data In 2014 March, the Subaru telescope started a large-area NB survey with HSC in a Subaru strategic program (SSP: Aihara et al. 2018a). This survey will construct a sample of LAEs at z ≃ 2.2, 5.7, 6.6, and 7.3 with four NB filters: NB387, NB816, NB921, and NB101. The statistical LAE sample allows us to study the LAE evolution and physical processes of the cosmic reionization. In this study, we use the HSC SSP S16A broadband (BB: Kawanomoto et al. 2017) and NB921 and NB816 data that were obtained in 2014–2016. Note that this HSC SSP S16A data is significantly larger than the data first released in Aihara et al. (2018b). The HSC images were reduced with the HSC pipeline, hscPipe 4.0.2 (Bosch et al. 2018), which is a program from the Large Synoptic Survey Telescope (LSST) software pipeline (Ivezic et al. 2008; Axelrod et al. 2010; Jurić et al. 2015). The photometric calibration was carried out with the PanSTARRS1 processing version 2 imaging survey data (Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013). The details of the data reduction are provided in Aihara et al. (2018b), Bosch et al. (2018), and Aihara et al. (2018b). The NB921 (NB816) filter has a central wavelength of λc = 9215 Å (8177 Å) and a full width at half maximum (FWHM) of 135 Å (113 Å), which traces the redshifted Lyα emission line at z = 6.580 ± 0.056 (z = 5.726 ± 0.046). The transmission curves and the detailed specifications of these NB filters are presented in Ouchi et al. (2018). The method for transmission curve measurement is given by Kawanomoto et al. (2017). The HSC SSP S16A NB921 and NB816 data cover a total survey area of ∼21.2 and ∼13.8 deg2, respectively. The survey area consists of two UltraDeep (UD) fields, UD-COSMOS and UD-SXDS, and three Deep (D) fields, D-ELAIS-N1, D-DEEP2-3, and D-COSMOS. The FWHM of the typical seeing size is ∼ 0$${^{\prime\prime}_{.}}$$6. The 5 σ NB limiting magnitudes for the UD and D fields are typically ∼25.5 and ∼25.0 mag in a 1$${^{\prime\prime}_{.}}$$5-diameter aperture, respectively. The details of the HSC NB data are presented in Shibuya et al. (2018). This HSC NB921 and NB816 data provide the largest NB survey area for z ≃ 5.7–6.6 LAEs even before the completion of the SSP observation. 2.2 Selection of bright LAEs Using the HSC NB data, we selected targets of bright LAE candidates with log LLyα/[erg s−1] ≃ 43–44 for follow-up spectroscopic observations. The details of the LAE selection are given in Shibuya et al. (2018), but we provide a brief description here. To identify objects with an NB magnitude excess in the HSC catalog, we applied magnitude and color selection criteria similar to those of Ouchi et al. (2008, 2010). To remove spurious sources such as satellite trails and cosmic rays, we performed visual inspections of multi-band HSC images of grizy and NB for the objects selected in the magnitude and color selection criteria. We also checked multi-epoch images to remove transients and asteroid-like moving objects. In total, photometric candidates of 1153 and 1077 LAEs at z ≃ 6.6 and z ≃ 5.7 were identified in the HSC NB921 and NB816 fields, respectively. Finally, we selected bright LAE candidates with an NB magnitude of NB ≤ 24 mag, corresponding to log LLyα/[erg s−1] ≃ 43–44. 3 Spectroscopic data We carried out optical and NIR spectroscopic observations for the bright LAE candidates at z ≃ 5.7–6.6 selected with the HSC NB data. These optical and NIR observations mainly (1) make spectroscopic confirmations through Lyα, and (2) investigate properties of ionizing sources (e.g., the presence of metal-poor galaxies and AGN activity) for bright LAEs. Table 1 summarizes the instruments, the exposure time, and line flux limits of our spectroscopic observations for each target. Table 1. Our optical and NIR spectroscopic observations for bright LAEs.* Object ID  Opt. inst.  Texp,opt  flim,opt  NIR inst.  Texp,NIR  flim,NIR      (min)  (erg s−1 cm−2)    (min)  (erg s−1 cm−2)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  HSC J162126+545719  FOCAS  60  ≃1.2 × 10−18  MOSFIRE  120  ≃1.8 × 10−18  HSC J233125−005216  LDSS3  90  ≃0.5 × 10−18  —  —  —  HSC J160234+545319  FOCAS  60  ≃0.3 × 10−18  nuMOIRCS  180  ≃5.3 × 10−18  HSC J160940+541409  FOCAS  60  ≃0.6 × 10−18  nuMOIRCS  300  ≃6.0 × 10−18  HSC J100334+024546  FOCAS  100  ≃1.3 × 10−18  —  —  —  HSC J100550+023401  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.3 × 10−18  HSC J160707+555347  FOCAS  60  ≃0.5 × 10−18  —  —  —  HSC J160107+550720  FOCAS  60  ≃0.3 × 10−18  —  —  —  HSC J233408+004403  FOCAS  60  ≃0.3 × 10−18  MOSFIRE  120  ≃0.8 × 10−18  HSC J021835−042321†  —  —  —  MOSFIRE  120  ≃1.5 × 10−18  HSC J233454+003603  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.6 × 10−18  HSC J021752−053511  FOCAS  60  ≃0.1 × 10−18  —  —  —  HSC J232558+002557  FOCAS  60  ≃0.2 × 10−18  —  —  —  HSC J022001−051637  LDSS3  45  ≃0.3 × 10−18  —  —  —  Object ID  Opt. inst.  Texp,opt  flim,opt  NIR inst.  Texp,NIR  flim,NIR      (min)  (erg s−1 cm−2)    (min)  (erg s−1 cm−2)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  HSC J162126+545719  FOCAS  60  ≃1.2 × 10−18  MOSFIRE  120  ≃1.8 × 10−18  HSC J233125−005216  LDSS3  90  ≃0.5 × 10−18  —  —  —  HSC J160234+545319  FOCAS  60  ≃0.3 × 10−18  nuMOIRCS  180  ≃5.3 × 10−18  HSC J160940+541409  FOCAS  60  ≃0.6 × 10−18  nuMOIRCS  300  ≃6.0 × 10−18  HSC J100334+024546  FOCAS  100  ≃1.3 × 10−18  —  —  —  HSC J100550+023401  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.3 × 10−18  HSC J160707+555347  FOCAS  60  ≃0.5 × 10−18  —  —  —  HSC J160107+550720  FOCAS  60  ≃0.3 × 10−18  —  —  —  HSC J233408+004403  FOCAS  60  ≃0.3 × 10−18  MOSFIRE  120  ≃0.8 × 10−18  HSC J021835−042321†  —  —  —  MOSFIRE  120  ≃1.5 × 10−18  HSC J233454+003603  FOCAS  60  ≃1.0 × 10−18  MOSFIRE  120  ≃0.6 × 10−18  HSC J021752−053511  FOCAS  60  ≃0.1 × 10−18  —  —  —  HSC J232558+002557  FOCAS  60  ≃0.2 × 10−18  —  —  —  HSC J022001−051637  LDSS3  45  ≃0.3 × 10−18  —  —  —  *(1) Object ID, sorted by the NB magnitude. (2) Instrument for optical spectroscopy. (3) Integration time for optical spectroscopy. (4) The 1 σ line flux sensitivity near Lyα emission lines. (5) Instrument for NIR spectroscopy. (6) Integration time for NIR spectroscopy. (7) Average values of the 1 σ line flux sensitivity at the expected wavelengths of C iv, He ii, and O iii]. †Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. View Large In subsections 3.1 and 3.2, we describe the details of the optical and NIR spectroscopic data, respectively. 3.1 Optical spectroscopic data We performed optical follow-up spectroscopy for bright LAE candidates at z ≃ 5.7–6.6 to detect Lyα emission lines. The choice of targets depended on the target visibility during the allocated time for individual spectroscopic observations. Basically, we selected the brightest LAE candidates as the targets in each observing run. 3.1.1 Subaru/FOCAS We used the Faint Object Camera and Spectrograph (FOCAS: Kashikawa et al. 2002) on the Subaru telescope to observe 16 LAE candidates. Out of the 16 objects, we observed 15 LAEs on 2016 June 21–22 and September 8 (S16A-060N and S16B-029N, PI: T. Shibuya), and one as a filler target of a FOCAS observation in 2015 December (S15B-059, PI: S. Yuma; see Yuma et al. 2017). These observations were made with the VPH900 grism with the O58 order-cut filter, giving spectral coverage of 7500–10450 Å with a dispersion of 0.74 Å pix−1. The 0$${^{\prime\prime}_{.}}$$8-wide slit used gave a spectroscopic resolution of R ≃ 1800, which is sufficient to distinguish [O ii] doublet lines from low-z galaxy contaminants at z ≃ 0.6–0.8. The observing nights were photometric, with good seeing of ∼ 0$${^{\prime\prime}_{.}}$$6–1$${^{\prime\prime}_{.}}$$0. The Multi-Object Spectroscopy (MOS) mode was used to securely align the slits on our high-z sources. Each of the 20 min exposures was taken by dithering the telescope pointing along the slit by ± 1$${^{\prime\prime}_{.}}$$0. The standard star Feige 34 was taken at the beginning and end of each observed night (Massey & Gronwall 1990). Our FOCAS spectra were reduced in a standard manner with the IRAF2 package (e.g., Kashikawa et al. 2006; Shibuya et al. 2012). First, we performed flat-fielding with flat images, corrected for the image distortion, calibrated wavelengths with sky OH lines, and rejected sources illuminated by cosmic ray injections. Next, we subtracted the sky background. Then, we stacked the two-dimensional (2D) spectra. From each item of 2D data, we then extracted one-dimensional (1D) spectra using an extraction width of ∼ ±0$${^{\prime\prime}_{.}}$$4– ± 0$${^{\prime\prime}_{.}}$$8 in the spatial direction of the slits. The extraction width was determined based on the extent of the targets and the seeing conditions during the observations. Similarly, these extraction widths were used for the data obtained from the other optical and NIR spectrographs (subsections 3.1 and 3.2). Finally, we carried out flux calibrations for the 1D spectra using the data of standard stars. The slit loss of the emission line flux was automatically corrected in the flux calibration. This is because we observed the standard stars in the observing configuration (i.e., slit width) and sky condition that were the same as those for our main targets. Note that our high-z main targets are point source-like objects whose slit loss is the same as standard stars. For this reason, we did not perform data reduction procedures for slit loss correction for our optical and NIR spectra in subsections 3.1 and 3.2. 3.1.2 Magellan/LDSS3 We also used the Low Dispersion Survey Spectrograph 3 (LDSS3) on the Magellan II (Clay) telescope in October 2016 (PI: M. Rauch) to take spectroscopy for two bright LAE candidates. The seeing was ∼ 0$${^{\prime\prime}_{.}}$$6–1$${^{\prime\prime}_{.}}$$0. We set the instrumental configuration to observe wavelength ranges of 8000–10000 Å. The spatial pixel scale was 0$${^{\prime\prime}_{.}}$$189 pix−1, and the spectral dispersion was 0.47 Å pix−1. The slit width is 0$${^{\prime\prime}_{.}}$$8. 3.1.3 Magellan/IMACS In addition to the Subaru/FOCAS and Magellan/LDSS3 observations, we used spectroscopic data obtained with the Inamori-Magellan Areal Camera and Spectrograph (IMACS; Dressler et al. 2011) on the Magellan I Baade Telescope. The observations were conducted for high-z galaxies in the SXDS field in 2007–2011 (PI: M. Ouchi; R. Higuchi et al. in preparation). In the HSC LAE and IMACS catalog matching, we obtained optical spectra for eight bright LAEs. 3.1.4 LAE spectroscopic confirmations In total, we newly confirm 21 bright LAEs with a clear Lyα emission line in our Subaru/FOCAS and Magellan/LDSS3 observations and our Magellan/IMACS data. The 1D and 2D optical spectra of the 21 bright LAEs are shown in figure 1. A prominent asymmetric emission line is found at ∼9210 Å and ∼8160 Å for each LAE at z ≃ 6.6 and z ≃ 5.7, respectively. These emission lines are detected at the ∼10 σ–20 σ significance levels. No other emission line feature is found in the range of the observed wavelengths. We obtain the redshift of the bright LAEs by fitting the symmetric Gaussian profile to the observed Lyα emission lines in the wavelength ranges where the flux drops to 70% of its peak value (Shibuya et al. 2014a). Figure 2 shows the NB magnitude and Lyα EW, which is obtained in subsection 4.1. As shown in figure 2, our newly confirmed bright LAEs are as bright as, e.g., Himiko and CR7. Fig. 1. View largeDownload slide Lyα spectra for the 21 newly identified bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The red and blue lines represent the Lyα spectra of the bright LAEs at z ≃ 6.6 and ≃ 5.7, respectively. The dashed gray curves indicate the transmission curves of NB921 and NB816. The solid gray lines denote the sky OH emission lines. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. (Color online) Fig. 1. View largeDownload slide Lyα spectra for the 21 newly identified bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The red and blue lines represent the Lyα spectra of the bright LAEs at z ≃ 6.6 and ≃ 5.7, respectively. The dashed gray curves indicate the transmission curves of NB921 and NB816. The solid gray lines denote the sky OH emission lines. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. (Color online) Fig. 2. View largeDownload slide NB magnitude and Lyα EW for LAEs at z ≃ 6.6 (left) and ≃ 5.7 (right). The red squares represent the 21 newly identified bright LAEs. The green diamonds indicate NB < 24 bright LAEs which have been spectroscopically confirmed by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The magenta filled circles present LAE candidates in HSC LAE catalogs constructed by Shibuya et al. (2018). The gray open circles denote LAE candidates found in SCam NB surveys (Ouchi et al. 2008, 2010). The objects with EW0,Lyα > 700 Å are plotted at EW0,Lyα = 700 Å. (Color online) Fig. 2. View largeDownload slide NB magnitude and Lyα EW for LAEs at z ≃ 6.6 (left) and ≃ 5.7 (right). The red squares represent the 21 newly identified bright LAEs. The green diamonds indicate NB < 24 bright LAEs which have been spectroscopically confirmed by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The magenta filled circles present LAE candidates in HSC LAE catalogs constructed by Shibuya et al. (2018). The gray open circles denote LAE candidates found in SCam NB surveys (Ouchi et al. 2008, 2010). The objects with EW0,Lyα > 700 Å are plotted at EW0,Lyα = 700 Å. (Color online) We also check whether our LAEs selected with the HSC data, HSC LAEs, are spectroscopically confirmed in previous studies for the COSMOS and SXDS fields (Murayama et al. 2007; Ouchi et al. 2008, 2010; Taniguchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). In spectroscopic samples obtained by the previous studies, we find 7 bright LAEs with NB < 24 mag and 69 faint ones with NB > 24 mag. In total, 96 LAEs are confirmed in our spectroscopic observations and the previous studies. Table 2 summarizes the number of spectroscopically confirmed HSC LAEs. Table 2. Number of spectroscopically confirmed HSC LAEs at z ≃ 5.7–6.6.* Sample  NLAE,spec  Spec. obs. or sample  (1)  (2)  (3)  Bright (NB < 24)  13  FOCAS, LDSS3  Bright (NB < 24)  8  IMACS  Bright (NB < 24)  7  Literature‡  Faint (NB > 24)†  68  LDSS3, IMACS, literature‡  Total  96  —  Sample  NLAE,spec  Spec. obs. or sample  (1)  (2)  (3)  Bright (NB < 24)  13  FOCAS, LDSS3  Bright (NB < 24)  8  IMACS  Bright (NB < 24)  7  Literature‡  Faint (NB > 24)†  68  LDSS3, IMACS, literature‡  Total  96  —  *(1) LAE sample. (2) Number of spectroscopically confirmed LAEs. (3) Instruments for observations and spectroscopic samples. †See tables 8 and 9 in the Appendix. ‡Murayama et al. (2007), Ouchi et al. (2008, 2010), Taniguchi et al. (2009), Mallery et al. (2012), Sobral et al. (2015), Hu et al. (2016). View Large The photometric properties and the HSC images for the bright LAEs are given in table 3 and figure 3, respectively. Although most of the bright LAEs are not detected in the blue bands of g and r, COLA1 is marginally detected in the r-band image at ∼2.5 σ. Fig. 3. View largeDownload slide HSC cutout images of the spectroscopically confirmed bright LAEs with NB < 24 mag at z ≃ 6.6 (left) and ≃ 5.7 (right). The seven objects at the bottom are the previously identified bright LAEs at z ≃ 6.6 (Ouchi et al. 2009; Sobral et al. 2015; Hu et al. 2016) and at z ≃ 5.7 (Mallery et al. 2012). The image size is 4″ × 4″. The scale of the flux density is arbitrary. (Color online) Fig. 3. View largeDownload slide HSC cutout images of the spectroscopically confirmed bright LAEs with NB < 24 mag at z ≃ 6.6 (left) and ≃ 5.7 (right). The seven objects at the bottom are the previously identified bright LAEs at z ≃ 6.6 (Ouchi et al. 2009; Sobral et al. 2015; Hu et al. 2016) and at z ≃ 5.7 (Mallery et al. 2012). The image size is 4″ × 4″. The scale of the flux density is arbitrary. (Color online) Table 3. Photometric properties of bright LAEs with spectroscopic redshifts.* Object ID  α (J2000.0)  δ (J2000.0)  zLyα  NB  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  NB921 (z ≃ 6.6)  HSC J162126+545719  16:21:26.51  +54:57:19.14  6.545  22.33 ± 0.02  >25.8  23.77 ± 0.18  22.92 ± 0.16  HSC J233125−005216  23:31:25.36  −00:52:16.36  6.559  23.17 ± 0.08  >26.6  25.34 ± 0.27  24.96 ± 0.37  HSC J160234+545319  16:02:34.77  +54:53:19.95  6.576  23.24 ± 0.05  >26.4  24.79 ± 0.26  >24.8  HSC J160940+541409  16:09:40.25  +54:14:09.04  6.564  23.52 ± 0.06  >26.4  25.45 ± 0.32  >24.7  HSC J100334+024546  10:03:34.66  +02:45:46.56  6.575  23.61 ± 0.05  >26.7  25.62 ± 0.27  24.97 ± 0.29  HSC J100550+023401  10:05:50.97  +02:34:01.51  6.573  23.71 ± 0.10  >26.4  25.15 ± 0.22  >25.3  HSC J160707+555347  16:07:07.48  +55:53:47.90  6.586  23.86 ± 0.09  >26.5  25.35 ± 0.32  >24.8  HSC J160107+550720  16:01:07.45  +55:07:20.63  6.563  23.96 ± 0.12  >26.4  >25.5  >24.4  NB816 (z ≃ 5.7)  HSC J233408+004403  23:34:08.79  +00:44:03.78  5.707  22.85 ± 0.04  25.40 ± 0.20  >25.8  >25.1  HSC J021835−042321†  02:18:35.94  −04:23:21.62  5.757  23.10 ± 0.06  25.38 ± 0.22  24.93 ± 0.19  25.23 ± 0.56  HSC J233454+003603  23:34:54.95  +00:36:03.99  5.732  23.16 ± 0.05  25.42 ± 0.19  25.60 ± 0.37  24.59 ± 0.28  HSC J021752−053511  02:17:52.63  −05:35:11.78  5.756  23.17 ± 0.05  25.24 ± 0.12  24.50 ± 0.14  24.42 ± 0.20  HSC J021828−051423†  02:18:28.87  −05:14:23.01  5.737  23.57 ± 0.04  26.25 ± 0.22  26.27 ± 0.38  >25.78  HSC J021724−053309†  02:17:24.02  −05:33:09.61  5.707  23.64 ± 0.08  >25.8  25.36 ± 0.29  >25.4  HSC J021859−052916†  02:18:59.92  −05:29:16.81  5.674  23.71 ± 0.06  25.17 ± 0.14  24.05 ± 0.09  24.00 ± 0.17  HSC J021836−053528†  02:18:36.37  −05:35:28.07  5.700  23.75 ± 0.06  25.95 ± 0.22  25.20 ± 0.21  24.88 ± 0.25  HSC J232558+002557  23:25:58.43  +00:25:57.53  5.703  23.78 ± 0.09  25.86 ± 0.22  25.29 ± 0.28  >24.9  HSC J022001−051637  02:20:01.10  −05:16:37.51  5.708  23.79 ± 0.04  26.04 ± 0.19  25.99 ± 0.30  >25.8  HSC J021827−044736†  02:18:27.44  −04:47:36.98  5.703  23.80 ± 0.08  26.93 ± 0.38  >26.3  >25.8  HSC J021830−051457†  02:18:30.53  −05:14:57.81  5.688  23.83 ± 0.05  25.93 ± 0.17  26.27 ± 0.38  >25.8  HSC J021624−045516†  02:16:24.70  −04:55:16.55  5.706  23.94 ± 0.06  26.24 ± 0.22  25.67 ± 0.23  >25.5  Previously identified bright LAEs  HSC J100235+021213†  10:02:35.38  +02:12:13.96  6.593  23.18 ± 0.03  >26.9  24.98 ± 0.12  25.29 ± 0.31  HSC J100058+014815§  10:00:58.00  +01:48:15.14  6.604  23.25 ± 0.03  >26.9  25.12 ± 0.13  24.48 ± 0.16  HSC J021757−050844‖  02:17:57.58  −05:08:44.63  6.595  23.50 ± 0.03  >27.4  25.77 ± 0.20  25.40 ± 0.27  HSC J100124+023145♯  10:01:24.79  +02:31:45.38  6.541  23.61 ± 0.03  >27.0  25.25 ± 0.14  25.64 ± 0.40  HSC J100109+021513**  10:01:09.72  +02:15:13.45  5.712  23.13 ± 0.02  25.77 ± 0.13  25.91 ± 0.21  25.97 ± 0.41  HSC J100129+014929**  10:01:29.07  +01:49:29.81  5.707  23.47 ± 0.02  25.87 ± 0.15  25.27 ± 0.13  25.30 ± 0.28  HSC J100123+015600**  10:01:23.84  +01:56:00.46  5.726  23.94 ± 0.03  26.43 ± 0.25  25.85 ± 0.21  >25.9  Object ID  α (J2000.0)  δ (J2000.0)  zLyα  NB  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  NB921 (z ≃ 6.6)  HSC J162126+545719  16:21:26.51  +54:57:19.14  6.545  22.33 ± 0.02  >25.8  23.77 ± 0.18  22.92 ± 0.16  HSC J233125−005216  23:31:25.36  −00:52:16.36  6.559  23.17 ± 0.08  >26.6  25.34 ± 0.27  24.96 ± 0.37  HSC J160234+545319  16:02:34.77  +54:53:19.95  6.576  23.24 ± 0.05  >26.4  24.79 ± 0.26  >24.8  HSC J160940+541409  16:09:40.25  +54:14:09.04  6.564  23.52 ± 0.06  >26.4  25.45 ± 0.32  >24.7  HSC J100334+024546  10:03:34.66  +02:45:46.56  6.575  23.61 ± 0.05  >26.7  25.62 ± 0.27  24.97 ± 0.29  HSC J100550+023401  10:05:50.97  +02:34:01.51  6.573  23.71 ± 0.10  >26.4  25.15 ± 0.22  >25.3  HSC J160707+555347  16:07:07.48  +55:53:47.90  6.586  23.86 ± 0.09  >26.5  25.35 ± 0.32  >24.8  HSC J160107+550720  16:01:07.45  +55:07:20.63  6.563  23.96 ± 0.12  >26.4  >25.5  >24.4  NB816 (z ≃ 5.7)  HSC J233408+004403  23:34:08.79  +00:44:03.78  5.707  22.85 ± 0.04  25.40 ± 0.20  >25.8  >25.1  HSC J021835−042321†  02:18:35.94  −04:23:21.62  5.757  23.10 ± 0.06  25.38 ± 0.22  24.93 ± 0.19  25.23 ± 0.56  HSC J233454+003603  23:34:54.95  +00:36:03.99  5.732  23.16 ± 0.05  25.42 ± 0.19  25.60 ± 0.37  24.59 ± 0.28  HSC J021752−053511  02:17:52.63  −05:35:11.78  5.756  23.17 ± 0.05  25.24 ± 0.12  24.50 ± 0.14  24.42 ± 0.20  HSC J021828−051423†  02:18:28.87  −05:14:23.01  5.737  23.57 ± 0.04  26.25 ± 0.22  26.27 ± 0.38  >25.78  HSC J021724−053309†  02:17:24.02  −05:33:09.61  5.707  23.64 ± 0.08  >25.8  25.36 ± 0.29  >25.4  HSC J021859−052916†  02:18:59.92  −05:29:16.81  5.674  23.71 ± 0.06  25.17 ± 0.14  24.05 ± 0.09  24.00 ± 0.17  HSC J021836−053528†  02:18:36.37  −05:35:28.07  5.700  23.75 ± 0.06  25.95 ± 0.22  25.20 ± 0.21  24.88 ± 0.25  HSC J232558+002557  23:25:58.43  +00:25:57.53  5.703  23.78 ± 0.09  25.86 ± 0.22  25.29 ± 0.28  >24.9  HSC J022001−051637  02:20:01.10  −05:16:37.51  5.708  23.79 ± 0.04  26.04 ± 0.19  25.99 ± 0.30  >25.8  HSC J021827−044736†  02:18:27.44  −04:47:36.98  5.703  23.80 ± 0.08  26.93 ± 0.38  >26.3  >25.8  HSC J021830−051457†  02:18:30.53  −05:14:57.81  5.688  23.83 ± 0.05  25.93 ± 0.17  26.27 ± 0.38  >25.8  HSC J021624−045516†  02:16:24.70  −04:55:16.55  5.706  23.94 ± 0.06  26.24 ± 0.22  25.67 ± 0.23  >25.5  Previously identified bright LAEs  HSC J100235+021213†  10:02:35.38  +02:12:13.96  6.593  23.18 ± 0.03  >26.9  24.98 ± 0.12  25.29 ± 0.31  HSC J100058+014815§  10:00:58.00  +01:48:15.14  6.604  23.25 ± 0.03  >26.9  25.12 ± 0.13  24.48 ± 0.16  HSC J021757−050844‖  02:17:57.58  −05:08:44.63  6.595  23.50 ± 0.03  >27.4  25.77 ± 0.20  25.40 ± 0.27  HSC J100124+023145♯  10:01:24.79  +02:31:45.38  6.541  23.61 ± 0.03  >27.0  25.25 ± 0.14  25.64 ± 0.40  HSC J100109+021513**  10:01:09.72  +02:15:13.45  5.712  23.13 ± 0.02  25.77 ± 0.13  25.91 ± 0.21  25.97 ± 0.41  HSC J100129+014929**  10:01:29.07  +01:49:29.81  5.707  23.47 ± 0.02  25.87 ± 0.15  25.27 ± 0.13  25.30 ± 0.28  HSC J100123+015600**  10:01:23.84  +01:56:00.46  5.726  23.94 ± 0.03  26.43 ± 0.25  25.85 ± 0.21  >25.9  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5) Total magnitudes of NB921 for z ≃ 6.6 LAEs and NB816 for z ≃ 5.7 LAEs. (6)–(8) Total magnitudes of i, z, and y bands. (6)–(8) 2 σ limiting magnitudes for undetected bands. †Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. †COLA1 in Hu et al. (2016). §CR7 in Sobral et al. (2015). ‖Himiko in Ouchi et al. (2009). ♯MASOSA in Sobral et al. (2015). **Spectroscopically confirmed in Mallery et al. (2012). View Large Combining our 21 newly identified and the 7 previously confirmed bright LAEs (i.e., Himiko, CR7, MASOSA, COLA1, and three z ≃ 5.7 objects from Mallery et al. 2012), we have constructed a sample of 28 bright LAEs. The HSC data and our observations have enlarged a spectroscopic sample of bright LAEs by a factor of four. The large sample allows for a statistical study on the physical properties of bright LAEs with log LLyα/[erg s−1] ≃ 43–44. 3.1.5 Contamination rates in the LAE candidates We estimate contamination rates, fcontami, in the HSC LAE candidates using the spectroscopic data. In our Subaru/FOCAS and Magellan/LDSS3 observations for 12 z ≃ 6.6 and 6 z ≃ 5.7 bright LAE candidates with NB <24 mag, we identify 4 and 1 low-z contaminants, respectively. Figure 4 presents the spectra and HSC cutout images for the low-z contaminants. All of the five contaminants are strong [O iii]λλ4959, 5007 emitters at z ≃ 0.6–0.8 with faint BB magnitudes. The Hβ and Hγ emission lines are not significantly detected in the short integration times (i.e., ≃ 20–40 min) of the FOCAS and LDSS3 observations. The photometric properties of these low-z contaminants are listed in table 4. We find that fcontami ≃ 33% (=4/12) and ≃ 17% (=1/6) for bright LAE candidates with NB < 24 mag at z ≃ 6.6 and z ≃ 5.7, respectively. Fig. 4. View largeDownload slide (Left) Spectra for the five low-z contaminants in the Subaru/FOCAS and Magellan/LDSS3 observations. The red arrows indicate the positions of [O iii]λλ4959,5007 emission lines. The dashed gray curves denote the transmission curves of NB921 and NB816. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. The y-axis represents the flux density in arbitrary units. (Right) HSC cutout images of the low-z contaminants. The image size is 4″ × 4″. The scale of the flux density is arbitrary. The photometric properties of the low-z contaminants are summarized in table 4. (Color online) Fig. 4. View largeDownload slide (Left) Spectra for the five low-z contaminants in the Subaru/FOCAS and Magellan/LDSS3 observations. The red arrows indicate the positions of [O iii]λλ4959,5007 emission lines. The dashed gray curves denote the transmission curves of NB921 and NB816. The x-axis indicates the wavelength observed in air. The heliocentric motion of the Earth is not corrected in this figure. The y-axis represents the flux density in arbitrary units. (Right) HSC cutout images of the low-z contaminants. The image size is 4″ × 4″. The scale of the flux density is arbitrary. The photometric properties of the low-z contaminants are summarized in table 4. (Color online) Table 4. Low-z contamination sources.* Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB  g  r  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10)  NB921  HSC J1001+0229  10:01:44.34  +02:29:09.96  0.840  23.64  26.78  >26.7  >26.5  25.10  >25.0  HSC J0957+0306  09:57:16.07  +03:06:30.31  0.841  23.73  >27.2  >26.7  >26.5  25.15  >25.0  HSC J1611+5541  16:11:30.34  +55:41:00.39  0.844  23.82  >27.2  >26.7  26.37  25.47  >25.0  HSC J1609+5620  16:09:18.03  +56:20:50.89  0.838  23.96  >27.2  >26.7  >26.5  25.52  >25.0  NB816  HSC J2327+0054  23:27:48.16  +00:54:20.84  0.639  23.18  >27.2  >26.7  25.31  >25.8  >25.0  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB  g  r  i  z  y    (hms)  (° ΄ ″)    (mag)  (mag)  (mag)  (mag)  (mag)  (mag)  (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10)  NB921  HSC J1001+0229  10:01:44.34  +02:29:09.96  0.840  23.64  26.78  >26.7  >26.5  25.10  >25.0  HSC J0957+0306  09:57:16.07  +03:06:30.31  0.841  23.73  >27.2  >26.7  >26.5  25.15  >25.0  HSC J1611+5541  16:11:30.34  +55:41:00.39  0.844  23.82  >27.2  >26.7  26.37  25.47  >25.0  HSC J1609+5620  16:09:18.03  +56:20:50.89  0.838  23.96  >27.2  >26.7  >26.5  25.52  >25.0  NB816  HSC J2327+0054  23:27:48.16  +00:54:20.84  0.639  23.18  >27.2  >26.7  25.31  >25.8  >25.0  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift. (5) Total magnitudes of NB921 for z ≃ 6.6 LAEs and NB816 for z ≃ 5.7 LAEs. (6)–(10) Total magnitudes of g, r, i, z, and y bands. (6)–(10) 2 σ limiting magnitudes for undetected bands. View Large We also calculate fcontami in the HSC LAE candidates including our Magellan/IMACS spectroscopic data (sub-subsection 3.1.3). This spectroscopic sample includes faint HSC LAE candidates with NB > 24 mag. Combining our Subaru/FOCAS and Magellan/LDSS3 data and the cross-matching of the Magellan/IMACS spectroscopic catalogs, we find that 28 and 53 HSC LAE candidates at z ≃ 6.6 and z ≃ 5.7 are spectroscopically observed. In total, we find that 4 out of 28 (4 out of 53) HSC LAE candidates are low-z contaminants, and estimate fcontami to be ≃ 14% and ≃ 8% for the samples of z ≃ 6.6 and z ≃ 5.7 LAEs, respectively. In these estimates with the spectroscopic data, we find that fcontami ≃ 0%–30%. Table 5 summarizes the contamination rates. These fcontami values are used for the contamination correction for, e.g., LAE clustering (Ouchi et al. 2018), Lyα LFs (Konno et al. 2018), and LAE overdensity (R. Higuchi et al. in preparation). Table 5. Contamination rates in the HSC LAE candidates.* Redshift  Nobs  Nlow-z  fcontami  Spec. obs.  (1)  (2)  (3)  (4)  (5)  Bright (NB < 24)  6.6  12  4  0.33  FOCAS,† LDSS3†  5.7  6  1  0.17  FOCAS,† LDSS3†  All  6.6  28  4  0.14  FOCAS,† LDSS3,†,‡ IMACS§  5.7  53  4  0.08  FOCAS,† LDSS3,† IMACS§  Redshift  Nobs  Nlow-z  fcontami  Spec. obs.  (1)  (2)  (3)  (4)  (5)  Bright (NB < 24)  6.6  12  4  0.33  FOCAS,† LDSS3†  5.7  6  1  0.17  FOCAS,† LDSS3†  All  6.6  28  4  0.14  FOCAS,† LDSS3,†,‡ IMACS§  5.7  53  4  0.08  FOCAS,† LDSS3,† IMACS§  *(1) Redshift of the LAE sample. (2) Number of spectroscopically observed HSC LAEs. (3) Number of low-z contaminants. (4) Contamination rates. (5) Spectroscopic follow-up observations. Only for the observations whose Nobs and Nlow-z are found. †This study. ‡Y. Harikane et al. (in preparation.) §R. Higuchi (in preparation). View Large 3.2 NIR spectroscopic data We performed deep NIR spectroscopy to investigate whether the rest-frame UV-nebular emission lines (i.e., C iv λλ1548, 1550, He ii λ1640, and O iii]λλ1661,1666) exist in bright LAEs. As a first attempt, we observed 7 out of the spectroscopically confirmed 21 bright LAEs. The LAEs observed by NIR spectrographs are listed in table 1. The choice of targets depended on the target visibility during the allocated time for the individual spectroscopic observations. Basically, we have selected the brightest LAEs as the targets in each observing run. 3.2.1 Keck/MOSFIRE We used the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE: McLean et al. 2012) on the Keck I telescope to observe four LAEs on 2016 September 9 (S16B-029N, PI: T. Shibuya) and an LAE on 2015 January 3–4 as a filler target (S15B-075, PI: M. Ouchi). Similar to the Subaru/FOCAS observations, the MOS mode was utilized to securely align the slits on our high-z sources. We used the Y- and J-band filters for LAEs at z ≃ 5.7 and z ≃ 6.6, respectively. The seeing size was ∼ 0$${^{\prime\prime}_{.}}$$5–0$${^{\prime\prime}_{.}}$$6. The 0$${^{\prime\prime}_{.}}$$8-wide slit was used, giving a spectral resolution of R ≃ 3500. The data for objects and standard stars were reduced using the MOSFIRE data reduction pipeline.3 We conducted standard reduction processes for the MOSFIRE spectra with sets of default pipeline parameters (see, e.g., Kojima et al. 2016). Using spectral type A stars which were taken in this observing run, we performed flux calibrations for the spectra of the target LAEs. 3.2.2 Subaru/nuMOIRCS We used the upgraded version of the Multi-Object InfraRed Camera and Spectrograph (nuMOIRCS; Ichikawa et al. 2006; Suzuki et al. 2008; Fabricius et al. 2016; Walawender et al. 2016) on the Subaru telescope on 2016 June 21–22 to observe two LAEs at z ≃ 6.6 (S16A-060N, PI: T. Shibuya). The MOS mode was used to securely align the slits on our high-z sources. There were thin sky cirrus clouds, but the weather conditions were photometric. The seeing size was ∼ 0$${^{\prime\prime}_{.}}$$5–1$${^{\prime\prime}_{.}}$$0. The width of each slit in the MOS masks is 0$${^{\prime\prime}_{.}}$$8. We used the VPH-J grism, giving a spectral resolution of R ≃ 3000. The standard star HIP115119 was observed on each night for flux calibrations. We reduced the nuMOIRCS spectra with IRAF in a manner similar to the FOCAS data reduction (sub-subsection 3.1.1). We performed bias subtraction, flat-fielding, image distortion correction, cosmic ray rejection, wavelength calibration, sky subtraction, and flux calibration. 4 Results 4.1 Physical properties We present the physical quantities related to the Lyα emission: Lyα flux, fLyα, Lyα luminosity, LLyα, and the rest-frame Lyα EW, EW0,Lyα, for the bright LAEs with a spectroscopic redshift. To obtain these quantities, we scale the observed Lyα spectra to match the NB and BB magnitudes. Here we assume the rest-frame UV spectral slope of β = −2. The β parameter is defined by fλ ∝ λβ, where fλ is a galaxy spectrum at ≃1500–3000 Å. The 2 σ lower limits of y- (z)-band magnitudes are used for z ≃ 6.6 (z ≃ 5.7) LAEs whose UV continuum emission is not detected. For HSC J162126+545719, whose UV continuum is detected in the spectroscopic data (see figure 1), we use the UV continuum flux density in the spectra to measure the EW0,Lyα and MUV values. Table 6 presents the quantities of fLyα, LLyα, and EW0,Lyα for our 21 bright LAEs, including a sample of 7 LAEs identified by previous studies (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). Figure 2 shows EW0,Lyα as a function of NB magnitude. The EW0,Lyα value ranges from ≃ 10 Å to ≃ 300 Å. Table 6. Physical properties of bright LAEs with spectroscopic redshifts. Object ID  FLyα  log LLyα  EW0,Lyα  ΔVFWHM  MUV  Extended?†    (erg s−1 cm−2)  (erg s−1)  (Å)  (km s−1)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J162126+545719  16.0 ± 0.12  43.89 ± 0.12  98.6 ± 32.7§ §  367 ± 19  −20.48 ± 0.31§ §    HSC J233125−005216  8.20 ± 0.05  43.60 ± 0.15  80.8 ± 33.4  168 ± 17  −21.87 ± 0.37    HSC J160234+545319  6.74 ± 0.03  43.52 ± 0.002  >57.3  394 ± 21  >−22.0    HSC J160940+541409  3.98 ± 0.06  43.29 ± 0.006  >30.8  302 ± 29  >−22.1  Y  HSC J100334+024546  6.14 ± 0.13  43.48 ± 0.18  61.1 ± 18.9  239 ± 18  −21.87 ± 0.29    HSC J100550+023401  7.94 ± 0.10  43.59 ± 0.005  >107.0  312 ± 34  >−21.5    HSC J160707+555347  6.07 ± 0.05  43.48 ± 0.004  >51.5  397 ± 30  >−22.0    HSC J160107+550720  2.45 ± 0.03  43.08 ± 0.005  >14.4  393 ± 33  >−22.4    NB816 (z ≃ 5.7)  HSC J233408+004403  13.5 ± 0.03  43.68 ± 0.001  >256.4  323 ± 18  >−20.8    HSC J021835−042321†  12.5 ± 0.07  43.66 ± 0.08  107.4 ± 21.4  298 ± 34  −21.70 ± 0.19    HSC J233454+003603  13.6 ± 0.10  43.69 ± 0.14  216.6 ± 88.5  318 ± 19  −21.02 ± 0.37    HSC J021752−053511  12.7 ± 0.09  43.66 ± 0.06  73.5 ± 10.7  157 ± 8  −22.13 ± 0.14    HSC J021828−051423†  7.04 ± 0.06  43.40 ± 0.15  207.3 ± 87.2  <410  −20.35 ± 0.38    HSC J021724−053309†  5.48 ± 0.02  43.29 ± 0.12  69.5 ± 21.9  <410  −21.25 ± 0.29    HSC J021859−052916†  4.55 ± 0.05  43.20 ± 0.04  17.2 ± 1.8  311 ± 44  −22.55 ± 0.09    HSC J021836−053528†  4.90 ± 0.03  43.24 ± 0.09  53.6 ± 11.8  <410  −21.41 ± 0.21    HSC J232558+002557  3.59 ± 0.02  43.10 ± 0.12  42.7 ± 13.1  373 ± 31  −21.32 ± 0.28    HSC J022001−051637  5.10 ± 0.03  43.26 ± 0.12  115.6 ± 37.1  271 ± 30  −20.62 ± 0.30    HSC J021827−044736†  5.34 ± 0.05  43.28 ± 0.03  >160.8  <410  >−20.3    HSC J021830−051457†  7.19 ± 0.13  43.40 ± 0.15  210.3 ± 88.8  <410  −20.34 ± 0.38    HSC J021624−045516†  4.17 ± 0.03  43.17 ± 0.09  70.5 ± 17.1  <410  −20.94 ± 0.23    Previously identified bright LAEs§  HSC J100235+021213‖  16.0  43.9  53  194  −21.55 ± 0.31    HSC J100058+014815♯  12.7 ± 0.08  43.8  211  266  −22.37 ± 0.16  Y  HSC J021757−050844**  5.06 ± 0.32  43.4  78  251  −21.44 ± 0.27  Y  HSC J100124+023145††  5.16  43.4  >206  386  −21.19 ± 0.40    HSC J100109+021513‡‡  7.32 ± 0.85  43.4  $$19.7^{+9.00}_{-7.93}$$  265 ± 71  −20.64 ± 0.41  Y  HSC J100129+014929‡‡  5.77 ± 0.61  43.3  $$60.9^{+5.89}_{-41.32}$$  422 ± 120  −21.31 ± 0.28  Y  HSC J100123+015600‡‡  3.79 ± 0.66  43.1  $$11.4^{+8.01}_{-7.32}$$  237 ± 58  >−20.72    Object ID  FLyα  log LLyα  EW0,Lyα  ΔVFWHM  MUV  Extended?†    (erg s−1 cm−2)  (erg s−1)  (Å)  (km s−1)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J162126+545719  16.0 ± 0.12  43.89 ± 0.12  98.6 ± 32.7§ §  367 ± 19  −20.48 ± 0.31§ §    HSC J233125−005216  8.20 ± 0.05  43.60 ± 0.15  80.8 ± 33.4  168 ± 17  −21.87 ± 0.37    HSC J160234+545319  6.74 ± 0.03  43.52 ± 0.002  >57.3  394 ± 21  >−22.0    HSC J160940+541409  3.98 ± 0.06  43.29 ± 0.006  >30.8  302 ± 29  >−22.1  Y  HSC J100334+024546  6.14 ± 0.13  43.48 ± 0.18  61.1 ± 18.9  239 ± 18  −21.87 ± 0.29    HSC J100550+023401  7.94 ± 0.10  43.59 ± 0.005  >107.0  312 ± 34  >−21.5    HSC J160707+555347  6.07 ± 0.05  43.48 ± 0.004  >51.5  397 ± 30  >−22.0    HSC J160107+550720  2.45 ± 0.03  43.08 ± 0.005  >14.4  393 ± 33  >−22.4    NB816 (z ≃ 5.7)  HSC J233408+004403  13.5 ± 0.03  43.68 ± 0.001  >256.4  323 ± 18  >−20.8    HSC J021835−042321†  12.5 ± 0.07  43.66 ± 0.08  107.4 ± 21.4  298 ± 34  −21.70 ± 0.19    HSC J233454+003603  13.6 ± 0.10  43.69 ± 0.14  216.6 ± 88.5  318 ± 19  −21.02 ± 0.37    HSC J021752−053511  12.7 ± 0.09  43.66 ± 0.06  73.5 ± 10.7  157 ± 8  −22.13 ± 0.14    HSC J021828−051423†  7.04 ± 0.06  43.40 ± 0.15  207.3 ± 87.2  <410  −20.35 ± 0.38    HSC J021724−053309†  5.48 ± 0.02  43.29 ± 0.12  69.5 ± 21.9  <410  −21.25 ± 0.29    HSC J021859−052916†  4.55 ± 0.05  43.20 ± 0.04  17.2 ± 1.8  311 ± 44  −22.55 ± 0.09    HSC J021836−053528†  4.90 ± 0.03  43.24 ± 0.09  53.6 ± 11.8  <410  −21.41 ± 0.21    HSC J232558+002557  3.59 ± 0.02  43.10 ± 0.12  42.7 ± 13.1  373 ± 31  −21.32 ± 0.28    HSC J022001−051637  5.10 ± 0.03  43.26 ± 0.12  115.6 ± 37.1  271 ± 30  −20.62 ± 0.30    HSC J021827−044736†  5.34 ± 0.05  43.28 ± 0.03  >160.8  <410  >−20.3    HSC J021830−051457†  7.19 ± 0.13  43.40 ± 0.15  210.3 ± 88.8  <410  −20.34 ± 0.38    HSC J021624−045516†  4.17 ± 0.03  43.17 ± 0.09  70.5 ± 17.1  <410  −20.94 ± 0.23    Previously identified bright LAEs§  HSC J100235+021213‖  16.0  43.9  53  194  −21.55 ± 0.31    HSC J100058+014815♯  12.7 ± 0.08  43.8  211  266  −22.37 ± 0.16  Y  HSC J021757−050844**  5.06 ± 0.32  43.4  78  251  −21.44 ± 0.27  Y  HSC J100124+023145††  5.16  43.4  >206  386  −21.19 ± 0.40    HSC J100109+021513‡‡  7.32 ± 0.85  43.4  $$19.7^{+9.00}_{-7.93}$$  265 ± 71  −20.64 ± 0.41  Y  HSC J100129+014929‡‡  5.77 ± 0.61  43.3  $$60.9^{+5.89}_{-41.32}$$  422 ± 120  −21.31 ± 0.28  Y  HSC J100123+015600‡‡  3.79 ± 0.66  43.1  $$11.4^{+8.01}_{-7.32}$$  237 ± 58  >−20.72    *(1) Object ID. (2) Lyα flux in units of 10−17 erg s−1 cm−2. (3) Lyα luminosity. (4) Lyα EW. (5) Velocity FWHM of the Lyα emission line. (6) Absolute UV magnitude. (7) Flag of the Lyα spatial extent. †If the column is Y, the object is spatially extended in Lyα. See Shibuya et al. (2018). ‡Spectroscopically confirmed with Magellan/IMACS. See sub-subsection 3.1.3. §Physical quantities in the columns (2)–(5) are obtained from the literature. ‖COLA1 in Hu et al. (2016). ♯CR7 in Sobral et al. (2015). **Himiko in Ouchi et al. (2009). ††MASOSA in Sobral et al. (2015). ‡‡Spectroscopically confirmed in Mallery et al. (2012). §§These values are calculated from the rest-frame UV continuum emission detected in the spectroscopic data. View Large Table 6 also shows whether the bright LAEs are spatially extended or not in Lyα based on our measurements of isophotal areas, Aiso (see Shibuya et al. 2018). We find that only 5 out of the 28 bright LAEs show spatially extended Lyα emission. The Aiso measurements indicate that Lyα emission of bright LAEs is typically compact. 4.2 Lyα line width To quantify the Lyα line profiles, we measure the FWHM velocity width, ΔVFWHM. We fit the symmetric Gaussian profile to the Lyα emission lines, and obtain the observed FWHM velocity width, ΔVobs, in the same manner as in Ouchi et al. (2010) for consistency. We correct for the instrumental broadening of line profile, and obtain ΔVFWHM by $$\Delta V_{\rm FWHM}=\sqrt{\Delta V_{\rm obs}^2 - \Delta V_{\rm inst}^2}$$, where ΔVobs and ΔVinst are the FWHM velocity widths for the observed Lyα lines and the instrumental resolution, respectively. We use the uncertainties in the χ2 minimization fit as the ΔVFWHM errors. The ΔVFWHM values are listed in table 6. Figure 5 presents ΔVFWHM as a function of LLyα. We find that the bright LAEs have ΔVFWHM ≃ 200–400 km s−1, similar to z ≃ 6 faint LAEs with log LLyα/[erg s−1] ≲ 43 (Ouchi et al. 2010). The narrow Lyα emission lines of ΔV ≃ 200–400 km s−1 indicate that the bright LAEs are not broad-line AGNs. Fig. 5. View largeDownload slide Lyα line FWHM as a function of Lyα luminosity. The red filled and open squares indicate our bright LAEs with Lyα emission line spectroscopically resolved and not resolved, respectively. The green filled diamonds denote bright LAEs which have been previously confirmed (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The black circles represent faint z ≃ 6.6 LAEs with log LLyα/[erg s−1] ≲ 43 in Ouchi et al. (2010). (Color online) Fig. 5. View largeDownload slide Lyα line FWHM as a function of Lyα luminosity. The red filled and open squares indicate our bright LAEs with Lyα emission line spectroscopically resolved and not resolved, respectively. The green filled diamonds denote bright LAEs which have been previously confirmed (Ouchi et al. 2009; Mallery et al. 2012; Sobral et al. 2015; Hu et al. 2016). The black circles represent faint z ≃ 6.6 LAEs with log LLyα/[erg s−1] ≲ 43 in Ouchi et al. (2010). (Color online) To quantify the relation between ΔVFWHM and LLyα in figure 5, we carry out Spearman rank correlation tests. In this test, we find a marginal correlation at the ∼1.7 σ significance level, possibly suggesting that ΔVFWHM increases with increasing LLyα. 4.3 X-ray, mid-IR, and radio detectability We check X-ray, mid-IR (MIR), and radio data to investigate whether the bright LAEs have a signature of AGN activities. Such X-ray, MIR, and radio data are available in the UD fields, UD-COSMOS and UD-SXDS. In UD-COSMOS, one object (i.e., HSC J100334+024546) is covered by MIR and radio data. In UD-SXDS, all ten objects are observed in X-ray, MIR, and radio. For the X-ray data, we use the XMM-Newton source catalog whose sensitivity limit is f0.5–2 keV = 6 × 10 − 16 erg cm−2 s−1 (Ueda et al. 2008). For the MIR data, we use the Spitzer/MIPS 24 μm source catalogs for UD-COSMOS (Sanders et al. 2007) and UD-SXDS (the SpUDS survey, PI: J. Dunlop). These Spitzer/MIPS 24 μm images reach 5 σ sensitivity limits of 21.2 mag in UD-COSMOS and 18.0 mag in UD-SXDS. For the radio data, we check the Very Large Array (VLA) 1.4 GHz source catalogs of Schinnerer et al. (2007) for UD-COSMOS and Simpson et al. (2006) for UD-SXDS. The typical r.m.s. noise level of the VLA data is f1.4 GHz ≃ 10 μJy beam−1. We find that there are no counterparts in the X-ray, MIR, and radio data, indicating that there is no clear signature of AGN activities based on the multi-wavelength data. By considering the typical spectral energy distribution of AGNs (e.g., Elvis et al. 1994; Telfer et al. 2002; Richards et al. 2003), the rest-frame UV luminosity of LAEs, and the sensitivity limits of these multi-wavelength data, we rule out the possibility that the LAEs have radio-loud AGNs. 4.4 UV-nebular line flux Here we investigate whether the rest-frame UV-nebular lines of N v λλ1238,1240, C iv λλ1548,1550, He ii λ1640, and O iii]λλ1661, 1666 are detected from the bright LAEs. First, we check the detectability of the N v emission line, which is a coarse indicator of AGN presence. The wavelengths of N v are covered by the FOCAS, LDSS3, and IMACS optical spectra for both of the z ≃ 6.6 and z ≃ 5.7 LAE samples. In order to estimate the flux limits, we sample the 1D spectra in ∼10 Å bins (comparable to the Lyα line FWHM) around the expected wavelengths of N v. We then obtain the flux limit by using the flux distribution over a ±50 Å range of the expected wavelengths of N v. We find that there are no N v emission lines for all the 21 bright LAEs. The 2 σ flux limits for the N v emission lines are listed in table 7. The line flux ratio of N v to Lyα is typically fNV/fLyα ≲ 10%. Table 7. UV-nebular emission lines of bright LAEs.* Object ID  Flux (EW0) (2 σ upper limits)  Line flux ratio relative to Lyα  (R.A.)  N v  C iv  He ii  O iii]  N v  C iv  He ii  O iii]      /Lyα  /Lyα  /Lyα  /Lyα    (10−17 erg s−1 cm−2) (Å)          (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  J162126  <0.81(<7.2)  <0.13(<1.8)  <0.35(<5.4)  <0.22(<3.5)  <0.05  <0.01  <0.02  <0.01  J233125  <0.53  —  —  —  <0.06  —  —  —  J160234  <0.71  <0.81  <1.06  <1.55  <0.11  <0.12  <0.16  <0.23  J160940  <0.56  <0.77  <1.20  <1.95  <0.14  <0.19  <0.30  <0.49  J100334  <0.75  —  —  —  <0.12  —  —  —  J100550  <0.64(<6.6)  <0.07(<1.1)  <0.05(0.91)  <0.16(<3.0)  <0.08  <0.01  <0.01  <0.03  J160707  <0.55  —  —  —  <0.09  —  —  —  J160107  <0.66  —  —  —  <0.27  —  —  —  J233408  <0.67  1.15(>42)  <0.16  <0.09  <0.05  0.08 ± 0.008  <0.01  <0.01  J021835  <0.92(<8.2)  <0.30(<4.2)  <0.39(<6.1)  <0.06(<1.0)  <0.07  <0.02  <0.03  <0.01  J233454  <0.64(<11)  <0.08(<2.1)  <0.12(<3.5)  <0.13(<3.9)  <0.05  <0.01  <0.01  <0.01  J201752  <0.70  —  —  —  <0.06  —  —  —  J021828  <0.62  —  —  —  <0.09  —  —  —  J021724  <0.15  —  —  —  <0.03  —  —  —  J021859  <0.59  —  —  —  <0.13  —  —  —  J021836  <0.26  —  —  —  <0.05  —  —  —  J232558  <0.45  —  —  —  <0.13  —  —  —  J022001  <0.72  —  —  —  <0.14  —  —  —  J021827  <1.05  —  —  —  <0.20  —  —  —  J021830  <1.24  —  —  —  <0.17  —  —  —  J021624  <0.43  —  —  —  <0.10  —  —  —  Object ID  Flux (EW0) (2 σ upper limits)  Line flux ratio relative to Lyα  (R.A.)  N v  C iv  He ii  O iii]  N v  C iv  He ii  O iii]      /Lyα  /Lyα  /Lyα  /Lyα    (10−17 erg s−1 cm−2) (Å)          (1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  J162126  <0.81(<7.2)  <0.13(<1.8)  <0.35(<5.4)  <0.22(<3.5)  <0.05  <0.01  <0.02  <0.01  J233125  <0.53  —  —  —  <0.06  —  —  —  J160234  <0.71  <0.81  <1.06  <1.55  <0.11  <0.12  <0.16  <0.23  J160940  <0.56  <0.77  <1.20  <1.95  <0.14  <0.19  <0.30  <0.49  J100334  <0.75  —  —  —  <0.12  —  —  —  J100550  <0.64(<6.6)  <0.07(<1.1)  <0.05(0.91)  <0.16(<3.0)  <0.08  <0.01  <0.01  <0.03  J160707  <0.55  —  —  —  <0.09  —  —  —  J160107  <0.66  —  —  —  <0.27  —  —  —  J233408  <0.67  1.15(>42)  <0.16  <0.09  <0.05  0.08 ± 0.008  <0.01  <0.01  J021835  <0.92(<8.2)  <0.30(<4.2)  <0.39(<6.1)  <0.06(<1.0)  <0.07  <0.02  <0.03  <0.01  J233454  <0.64(<11)  <0.08(<2.1)  <0.12(<3.5)  <0.13(<3.9)  <0.05  <0.01  <0.01  <0.01  J201752  <0.70  —  —  —  <0.06  —  —  —  J021828  <0.62  —  —  —  <0.09  —  —  —  J021724  <0.15  —  —  —  <0.03  —  —  —  J021859  <0.59  —  —  —  <0.13  —  —  —  J021836  <0.26  —  —  —  <0.05  —  —  —  J232558  <0.45  —  —  —  <0.13  —  —  —  J022001  <0.72  —  —  —  <0.14  —  —  —  J021827  <1.05  —  —  —  <0.20  —  —  —  J021830  <1.24  —  —  —  <0.17  —  —  —  J021624  <0.43  —  —  —  <0.10  —  —  —  *(1) Object ID. (2)–(5) Flux and 2 σ flux upper limits of the C iv, He ii, and O iii] emission lines. The numbers in parentheses are the EW and 2 σ limits of the C iv, He ii, and O iii] emission lines. (6)–(9) Line flux ratios of the UV-nebular emission lines relative to Lyα. View Large Table 8. Spectroscopically confirmed z ≃ 6.6 LAEs with NB > 24 mag.* Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB921  y  Reference    (hms)  (° ΄ ″)    (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J021843−050915  02:18:43.62  −05:09:15.63  6.510  24.33  24.87  Hari  HSC J021703−045619  02:17:03.46  −04:56:19.07  6.589  24.45  25.42  O10  HSC J021827−043507  02:18:27.01  −04:35:07.92  6.511  24.56  25.32  O10  HSC J021844−043636  02:18:44.64  −04:36:36.21  6.621  24.63  27.34  H  HSC J021702−050604  02:17:02.56  −05:06:04.61  6.545  24.64  26.35  O10  HSC J021826−050726  02:18:27.00  −05:07:26.89  6.554  24.69  —  O10  HSC J021819−050900  02:18:19.39  −05:09:00.65  6.563  24.73  26.04  O10  HSC J021654−045556  02:16:54.54  −04:55:56.94  6.617  24.82  25.67  O10  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB921  y  Reference    (hms)  (° ΄ ″)    (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB921 (z ≃ 6.6)  HSC J021843−050915  02:18:43.62  −05:09:15.63  6.510  24.33  24.87  Hari  HSC J021703−045619  02:17:03.46  −04:56:19.07  6.589  24.45  25.42  O10  HSC J021827−043507  02:18:27.01  −04:35:07.92  6.511  24.56  25.32  O10  HSC J021844−043636  02:18:44.64  −04:36:36.21  6.621  24.63  27.34  H  HSC J021702−050604  02:17:02.56  −05:06:04.61  6.545  24.64  26.35  O10  HSC J021826−050726  02:18:27.00  −05:07:26.89  6.554  24.69  —  O10  HSC J021819−050900  02:18:19.39  −05:09:00.65  6.563  24.73  26.04  O10  HSC J021654−045556  02:16:54.54  −04:55:56.94  6.617  24.82  25.67  O10  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5)–(6) Total magnitudes of NB921 and y band. (7) Reference (O10: Ouchi et al. 2010; Hari: Y. Harikane in preparation; H: R. Higuchi in preparation). Note that the magnitudes are values directly obtained from the HSC catalog. View Large Table 9. Spectroscopically confirmed z ≃ 5.7 LAEs with NB > 24 mag. Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB816  z  Reference          (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB816 (z ≃ 5.7)  HSC J095952+013723  09:59:52.13  +01:37:23.24  5.724  24.07  25.76  M12  HSC J021758−043030  02:17:58.91  −04:30:30.42  5.689  24.07  25.56  H  HSC J095933+024955  09:59:33.44  +02:49:55.92  5.724  24.10  27.25  M12  HSC J021749−052854  02:17:49.11  −05:28:54.17  5.694  24.10  26.77  O08  HSC J021704−052714  02:17:04.30  −05:27:14.30  5.686  24.11  26.29  H  HSC J095952+015005  09:59:52.03  +01:50:05.95  5.744  24.11  25.10  M12  HSC J021737−043943  02:17:37.96  −04:39:43.02  5.755  24.11  25.63  H  HSC J100015+020056  10:00:15.66  +02:00:56.04  5.718  24.15  26.08  M12  HSC J021734−044558  02:17:34.57  −04:45:58.95  5.702  24.20  25.44  H  HSC J100131+023105  10:01:31.08  +02:31:05.77  5.690  24.23  26.15  M12  HSC J100301+020236  10:03:01.15  +02:02:36.04  5.682  24.24  24.58  M12  HSC J021654−052155  02:16:54.60  −05:21:55.52  5.712  24.24  26.49  H  HSC J021748−053127  02:17:48.46  −05:31:27.02  5.690  24.25  25.67  O08  HSC J100127+023005  10:01:27.77  +02:30:05.83  5.696  24.28  25.61  M12  HSC J021745−052936  02:17:45.24  −05:29:36.01  5.688  24.30  27.26  O08  HSC J021725−050737  02:17:25.90  −05:07:37.59  5.704  24.35  26.21  H  HSC J100208+015444  10:02:08.80  +01:54:44.99  5.676  24.36  25.65  M12  HSC J095954+021039  09:59:54.77  +02:10:39.26  5.662  24.38  25.63  M12  HSC J095950+025406  09:59:50.09  +02:54:06.16  5.726  24.39  26.59  M12  HSC J022013−045109  02:20:13.33  −04:51:09.40  5.744  24.40  25.88  O08  HSC J100126+014430  10:01:26.88  +01:44:30.29  5.686  24.41  25.96  M12  HSC J095919+020322  09:59:19.74  +02:03:22.02  5.704  24.41  26.84  M12  HSC J095954+021516  09:59:54.52  +02:15:16.50  5.688  24.43  25.95  M12  HSC J021849−052235  02:18:49.00  −05:22:35.35  5.719  24.45  25.64  H  HSC J100005+020717  10:00:05.06  +02:07:17.01  5.704  24.46  26.64  M12  HSC J021830−052950  02:18:30.75  −05:29:50.34  5.707  24.46  28.89  H  HSC J100306+014742  10:03:06.13  +01:47:42.69  5.680  24.52  26.54  M12  HSC J021804−052147  02:18:04.17  −05:21:47.25  5.734  24.54  25.20  H  HSC J100022+024103  10:00:22.51  +02:41:03.25  5.661  24.55  25.34  M12  HSC J021848−051715  02:18:48.23  −05:17:15.45  5.741  24.56  25.45  H  HSC J021750−050203  02:17:50.86  −05:02:03.24  5.708  24.57  26.48  H  HSC J021526−045229  02:15:26.22  −04:52:29.93  5.655  24.62  24.95  H  HSC J021636−044723  02:16:36.44  −04:47:23.68  5.718  24.63  26.57  H  HSC J100030+021714  10:00:30.41  +02:17:14.73  5.695  24.65  26.70  M12  HSC J021558−045301  02:15:58.49  −04:53:01.75  5.718  24.68  26.55  H  HSC J021719−043150  02:17:19.13  −04:31:50.64  5.735  24.68  27.87  H  HSC J021822−042925  02:18:22.91  −04:29:25.89  5.697  24.68  27.65  H  HSC J100131+014320  10:01:31.11  +01:43:20.50  5.728  24.70  26.45  M12  HSC J095944+020050  09:59:44.07  +02:00:50.74  5.688  24.71  26.18  M12  HSC J021709−050329  02:17:09.77  −05:03:29.18  5.709  24.74  26.52  H  HSC J021803−052643  02:18:03.87  −05:26:43.45  5.747  24.75  27.66  H  HSC J100309+015352  10:03:09.81  +01:53:52.36  5.705  24.76  26.61  M12  HSC J021805−052704  02:18:05.17  −05:27:04.06  5.746  24.77  31.43  H  HSC J021739−043837  02:17:39.25  −04:38:37.21  5.720  24.79  27.00  H  HSC J100040+021903  10:00:40.24  +02:19:03.70  5.719  24.81  26.96  M12  HSC J021857−045648  02:18:57.32  −04:56:48.88  5.681  24.85  27.11  H  HSC J021745−044129  02:17:45.74  −04:41:29.24  5.674  24.86  27.34  H  HSC J021639−051346  02:16:39.89  −05:13:46.75  5.702  24.87  26.98  H  HSC J021805−052026  02:18:05.28  −05:20:26.90  5.742  24.87  26.10  H  HSC J021755−043251  02:17:55.40  −04:32:51.54  5.691  24.91  27.26  H  HSC J100058+013642  10:00:58.41  +01:36:42.89  5.688  24.91  27.97  M12  HSC J100029+015000  10:00:29.58  +01:50:00.78  5.707  24.97  26.80  M12  HSC J021911−045707  02:19:11.03  −04:57:07.48  5.704  25.00  27.46  H  HSC J021551−045325  02:15:51.34  −04:53:25.44  5.710  25.02  26.76  H  HSC J021625−045237  02:16:25.64  −04:52:37.18  5.728  25.07  —  H  HSC J021751−053003  02:17:51.14  −05:30:03.64  5.712  25.10  26.99  O08  HSC J021628−050103  02:16:28.05  −05:01:03.85  5.692  25.17  27.23  H  HSC J021943−044914  02:19:43.91  −04:49:14.30  5.684  25.17  26.86  H  HSC J100029+024115  10:00:29.13  +02:41:15.70  5.735  25.22  28.30  M12  HSC J100107+015222  10:01:07.35  +01:52:22.88  5.668  25.33  26.42  M12  Object ID  α (J2000.0)  δ (J2000.0)  zspec  NB816  z  Reference          (mag)  (mag)    (1)  (2)  (3)  (4)  (5)  (6)  (7)  NB816 (z ≃ 5.7)  HSC J095952+013723  09:59:52.13  +01:37:23.24  5.724  24.07  25.76  M12  HSC J021758−043030  02:17:58.91  −04:30:30.42  5.689  24.07  25.56  H  HSC J095933+024955  09:59:33.44  +02:49:55.92  5.724  24.10  27.25  M12  HSC J021749−052854  02:17:49.11  −05:28:54.17  5.694  24.10  26.77  O08  HSC J021704−052714  02:17:04.30  −05:27:14.30  5.686  24.11  26.29  H  HSC J095952+015005  09:59:52.03  +01:50:05.95  5.744  24.11  25.10  M12  HSC J021737−043943  02:17:37.96  −04:39:43.02  5.755  24.11  25.63  H  HSC J100015+020056  10:00:15.66  +02:00:56.04  5.718  24.15  26.08  M12  HSC J021734−044558  02:17:34.57  −04:45:58.95  5.702  24.20  25.44  H  HSC J100131+023105  10:01:31.08  +02:31:05.77  5.690  24.23  26.15  M12  HSC J100301+020236  10:03:01.15  +02:02:36.04  5.682  24.24  24.58  M12  HSC J021654−052155  02:16:54.60  −05:21:55.52  5.712  24.24  26.49  H  HSC J021748−053127  02:17:48.46  −05:31:27.02  5.690  24.25  25.67  O08  HSC J100127+023005  10:01:27.77  +02:30:05.83  5.696  24.28  25.61  M12  HSC J021745−052936  02:17:45.24  −05:29:36.01  5.688  24.30  27.26  O08  HSC J021725−050737  02:17:25.90  −05:07:37.59  5.704  24.35  26.21  H  HSC J100208+015444  10:02:08.80  +01:54:44.99  5.676  24.36  25.65  M12  HSC J095954+021039  09:59:54.77  +02:10:39.26  5.662  24.38  25.63  M12  HSC J095950+025406  09:59:50.09  +02:54:06.16  5.726  24.39  26.59  M12  HSC J022013−045109  02:20:13.33  −04:51:09.40  5.744  24.40  25.88  O08  HSC J100126+014430  10:01:26.88  +01:44:30.29  5.686  24.41  25.96  M12  HSC J095919+020322  09:59:19.74  +02:03:22.02  5.704  24.41  26.84  M12  HSC J095954+021516  09:59:54.52  +02:15:16.50  5.688  24.43  25.95  M12  HSC J021849−052235  02:18:49.00  −05:22:35.35  5.719  24.45  25.64  H  HSC J100005+020717  10:00:05.06  +02:07:17.01  5.704  24.46  26.64  M12  HSC J021830−052950  02:18:30.75  −05:29:50.34  5.707  24.46  28.89  H  HSC J100306+014742  10:03:06.13  +01:47:42.69  5.680  24.52  26.54  M12  HSC J021804−052147  02:18:04.17  −05:21:47.25  5.734  24.54  25.20  H  HSC J100022+024103  10:00:22.51  +02:41:03.25  5.661  24.55  25.34  M12  HSC J021848−051715  02:18:48.23  −05:17:15.45  5.741  24.56  25.45  H  HSC J021750−050203  02:17:50.86  −05:02:03.24  5.708  24.57  26.48  H  HSC J021526−045229  02:15:26.22  −04:52:29.93  5.655  24.62  24.95  H  HSC J021636−044723  02:16:36.44  −04:47:23.68  5.718  24.63  26.57  H  HSC J100030+021714  10:00:30.41  +02:17:14.73  5.695  24.65  26.70  M12  HSC J021558−045301  02:15:58.49  −04:53:01.75  5.718  24.68  26.55  H  HSC J021719−043150  02:17:19.13  −04:31:50.64  5.735  24.68  27.87  H  HSC J021822−042925  02:18:22.91  −04:29:25.89  5.697  24.68  27.65  H  HSC J100131+014320  10:01:31.11  +01:43:20.50  5.728  24.70  26.45  M12  HSC J095944+020050  09:59:44.07  +02:00:50.74  5.688  24.71  26.18  M12  HSC J021709−050329  02:17:09.77  −05:03:29.18  5.709  24.74  26.52  H  HSC J021803−052643  02:18:03.87  −05:26:43.45  5.747  24.75  27.66  H  HSC J100309+015352  10:03:09.81  +01:53:52.36  5.705  24.76  26.61  M12  HSC J021805−052704  02:18:05.17  −05:27:04.06  5.746  24.77  31.43  H  HSC J021739−043837  02:17:39.25  −04:38:37.21  5.720  24.79  27.00  H  HSC J100040+021903  10:00:40.24  +02:19:03.70  5.719  24.81  26.96  M12  HSC J021857−045648  02:18:57.32  −04:56:48.88  5.681  24.85  27.11  H  HSC J021745−044129  02:17:45.74  −04:41:29.24  5.674  24.86  27.34  H  HSC J021639−051346  02:16:39.89  −05:13:46.75  5.702  24.87  26.98  H  HSC J021805−052026  02:18:05.28  −05:20:26.90  5.742  24.87  26.10  H  HSC J021755−043251  02:17:55.40  −04:32:51.54  5.691  24.91  27.26  H  HSC J100058+013642  10:00:58.41  +01:36:42.89  5.688  24.91  27.97  M12  HSC J100029+015000  10:00:29.58  +01:50:00.78  5.707  24.97  26.80  M12  HSC J021911−045707  02:19:11.03  −04:57:07.48  5.704  25.00  27.46  H  HSC J021551−045325  02:15:51.34  −04:53:25.44  5.710  25.02  26.76  H  HSC J021625−045237  02:16:25.64  −04:52:37.18  5.728  25.07  —  H  HSC J021751−053003  02:17:51.14  −05:30:03.64  5.712  25.10  26.99  O08  HSC J021628−050103  02:16:28.05  −05:01:03.85  5.692  25.17  27.23  H  HSC J021943−044914  02:19:43.91  −04:49:14.30  5.684  25.17  26.86  H  HSC J100029+024115  10:00:29.13  +02:41:15.70  5.735  25.22  28.30  M12  HSC J100107+015222  10:01:07.35  +01:52:22.88  5.668  25.33  26.42  M12  *(1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of Lyα emission line. (5)–(6) Total magnitudes of NB816 and z-bands. (7) Reference (M12: Mallery et al. 2012; O08: Ouchi et al. 2008; H: R. Higuchi in preparation). Note that the magnitudes are values directly obtained from the HSC catalog. View Large Next, we search for the UV-nebular emission lines of C iv, He ii, and O iii] for the seven bright LAEs whose NIR spectra were obtained (subsection 3.2). Figure 6 presents the NIR spectra for the seven LAEs. Even in the deep NIR spectra with a 3 σ line flux sensitivity limit of ∼2 × 10−18 erg s−1 cm−2, we find no significant emission features at the expected wavelengths of redshifted He ii, C iv, and O iii] lines, except for a tentative C iv detection from a z ≃ 5.7 LAE, HSC J233408+004403 (see below in this section). The flux limits for the C iv, He ii, and O iii] emission lines are estimated in the same manner as that for N v. To estimate the detection limits, we assume a single emission line even for the C iv and O iii] doublets which are resolved in the spectral resolution of MOSFIRE and nuMOIRCS. The 2 σ flux limits for individual UV-nebular emission lines are listed in table 7. Fig. 6. View largeDownload slide NIR spectra for the bright LAEs at z ≃ 6.6 (the upper four spectra) and ≃ 5.7 (the lower three spectra). The left figures are three-color composite images of the bright LAEs. The blue ticks denote the C iv (left), He ii (center), and O iii] (right) wavelengths which are expected from the redshift of Lyα emission lines. For HSC J162126+545719, the emission feature near the expected C iv λ1550 wavelength is likely to be a residual of the sky subtraction, which is marked by a black cross. A C iv λ1550 emission line is tentatively detected in the spectrum of HSC J233408+004403 (see figure 7), which is discussed in subsection 5.3. (Color online) Fig. 6. View largeDownload slide NIR spectra for the bright LAEs at z ≃ 6.6 (the upper four spectra) and ≃ 5.7 (the lower three spectra). The left figures are three-color composite images of the bright LAEs. The blue ticks denote the C iv (left), He ii (center), and O iii] (right) wavelengths which are expected from the redshift of Lyα emission lines. For HSC J162126+545719, the emission feature near the expected C iv λ1550 wavelength is likely to be a residual of the sky subtraction, which is marked by a black cross. A C iv λ1550 emission line is tentatively detected in the spectrum of HSC J233408+004403 (see figure 7), which is discussed in subsection 5.3. (Color online) Our deep NIR spectroscopy indicates that there are no significant detections of UV-nebular emission lines for bright LAEs. By visual inspection for the NIR spectra, we find a tentative detection of the C iv λ1550 emission line from the brightest LAE in the z ≃ 5.7 sample, HSC J233408+004403. Figure 7 shows the NIR spectra around the wavelengths of the C iv emission line doublet for HSC J233408+004403. The C iv λ1550 emission line is tentatively detected at the ∼4 σ–9 σ significance level. The significance of the line detection depends on the wavelength range of flux integration. We also identify two negative C iv λ1550 emission lines which could originate from the ±3″ slit dithering processes in the MOSFIRE observation. Moreover, the tentative C iv λ1550 detection might explain a possible magnitude excess in the y-band covering the C iv wavelength (see figure 3). The line flux is ∼1.2 × 10−17 erg cm−2 s−1. The emission line has a velocity width of ΔVFWHM ≃ 50 km s−1, which is marginally resolved in the MOSFIRE spectral resolution. We do not detect the C iv λ1548 component of the C iv doublet from HSC J233408+004403. The single C iv emission line at λrest ≃ 1550 Å may be formed by a combination of absorption and emission lines that could originate from stellar winds and ISM. Such a C iv line profile has been found for z ≃ 1–3 galaxies (e.g., Shapley et al. 2003; Erb et al. 2010; Du et al. 2016). We discuss the emission line properties of the C iv emitter in subsection 5.3. Fig. 7. View largeDownload slide Tentative detection of a C iv λ1550 emission line for HSC J233408+004403. The 2D spectra in the top and middle panels present the S/N and flux maps, respectively. The bottom panel shows the 1D spectrum of the flux map. The white arrows indicate the expected positions of the negative C iv λ1550 emission lines which are produced in the ±3″ slit dithering processes. The top-left panel depicts the 1D S/N spectrum along the spatial direction at the tentative C iv λ1550 emission line. The blue ticks and the red arrows indicate the C iv λ1548 and C iv λ1550 wavelengths expected from the Lyα emission line (i.e., zLyα = 5.707). The cyan dashed line shows the OH sky emission. The C iv λ1550 emission line is tentatively detected at a significance level of ∼4–9. (Color online) Fig. 7. View largeDownload slide Tentative detection of a C iv λ1550 emission line for HSC J233408+004403. The 2D spectra in the top and middle panels present the S/N and flux maps, respectively. The bottom panel shows the 1D spectrum of the flux map. The white arrows indicate the expected positions of the negative C iv λ1550 emission lines which are produced in the ±3″ slit dithering processes. The top-left panel depicts the 1D S/N spectrum along the spatial direction at the tentative C iv λ1550 emission line. The blue ticks and the red arrows indicate the C iv λ1548 and C iv λ1550 wavelengths expected from the Lyα emission line (i.e., zLyα = 5.707). The cyan dashed line shows the OH sky emission. The C iv λ1550 emission line is tentatively detected at a significance level of ∼4–9. (Color online) 4.5 Reanalysis of CR7 spectra We investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He ii is claimed by Sobral et al. (2015). Two of the authors in this paper and the ESO-archive service reanalyzed the VLT/X-SHOOTER data that were used in the study of Sobral et al. (2015). We applied three methods to our reanalysis: (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D). We smooth our reduced X-SHOOTER spectra with a kernel of ∼0.4 Å width, which corresponds to that of Sobral et al. (2015). Figure 8 presents our reduced X-SHOOTER data for the optical (the left panel) and NIR (the right panel) arms for CR7 with the 1D spectrum obtained by Sobral et al. (2015). As shown in the left panel of figure 8, we clearly identify a Lyα emission line at λrest = 1216 Å. The Lyα line profiles of our data are in good agreement with that of the Sobral et al.’s optical spectrum. However, we find no signal at λrest = 1640 Å, where Sobral et al. (2015) find the emission line feature (the right panel of figure 8). The detection significance is <1 σ at λrest = 1640 Å in our NIR spectra. Instead, our NIR spectra show a feature of two possible peaks at λrest = 1643 Å, which is redder than the He ii wavelength of Sobral et al. (2015) by Δλrest ≃ 3 Å, corresponding to the redshift difference of Δz = 0.01. If we regard the two possible peaks as He ii, we obtain a detection significance of ∼1.8 σ. This significance value is inconsistent with the 6 σ detection of Sobral et al. (2015). Moreover, the red component of the two possible peaks appears to be made by sky subtraction residuals, as shown in figure 8a. In the case that this red component is masked for the line flux calculation, the detection significance decreases to ∼1.1 σ. To obtain all the values of detection significance and noise levels, we use OH sky line-free regions. Fig. 8. View largeDownload slide Reanalyzed VLT/X-SHOOTER spectra of CR7. The left and right panels denote the VIS and NIR arms of the X-SHOOTER spectra. The blue lines indicate the X-SHOOTER spectra in Sobral et al. (2015). The red, magenta, and orange lines depict spectra obtained from (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D), respectively. These lines have been smoothed with a kernel of ∼0.4 Å width, which is similar to that of Sobral et al. (2015). The gray lines present the unsmoothed spectrum obtained from our data reduction with ESO REFLEX. The thin blue and red lines indicate sky OH lines in Sobral et al. (2015) and our reanalyzed data, respectively. The top-left panels show the 2D spectrum of the X-SHOOTER VIS arm. The top-right panels indicate (a) sky OH line, (b) unsmoothed, and (c) smoothed 2D spectra, all of which are obtained from our data reduction with ESO REFLEX. The feature at λrest = 1643 Å appears to be made by sky subtraction residuals. The blue ticks indicate the position of He ii, whose detection is claimed by Sobral et al. (2015). See subsection 4.5 for more details. (Color online) Fig. 8. View largeDownload slide Reanalyzed VLT/X-SHOOTER spectra of CR7. The left and right panels denote the VIS and NIR arms of the X-SHOOTER spectra. The blue lines indicate the X-SHOOTER spectra in Sobral et al. (2015). The red, magenta, and orange lines depict spectra obtained from (1) reducing the raw data with the X-SHOOTER reduction pipeline ESO REFLEX (Pipeline), (2) stacking of each 2D single-exposure spectrum reduced by ESO (ESO 2D), and (3) stacking of each 1D single-exposure spectrum reduced by ESO (ESO 1D), respectively. These lines have been smoothed with a kernel of ∼0.4 Å width, which is similar to that of Sobral et al. (2015). The gray lines present the unsmoothed spectrum obtained from our data reduction with ESO REFLEX. The thin blue and red lines indicate sky OH lines in Sobral et al. (2015) and our reanalyzed data, respectively. The top-left panels show the 2D spectrum of the X-SHOOTER VIS arm. The top-right panels indicate (a) sky OH line, (b) unsmoothed, and (c) smoothed 2D spectra, all of which are obtained from our data reduction with ESO REFLEX. The feature at λrest = 1643 Å appears to be made by sky subtraction residuals. The blue ticks indicate the position of He ii, whose detection is claimed by Sobral et al. (2015). See subsection 4.5 for more details. (Color online) In our careful reanalysis for the X-SHOOTER data, we find that no He ii signal of CR7 is detected. This supports weak UV-nebular lines of the bright LAEs even for CR7. Based on our S/N-based reanalysis and the flux error from Sobral et al. (2015), we obtain 3 σ upper limits of He ii flux and EW for CR7, $$f_{\rm He\,{\scriptscriptstyle II}}<2.1\times 10^{-17}\:$$erg s−1 cm−2 and $$EW_{\rm He\,{\scriptscriptstyle II}}< 60$$ Å, respectively.4 4.6 Line flux ratios Figure 9 presents the line flux ratios of He ii/Lyα and C iv/Lyα for our bright LAEs and several Lyα-emitting populations such as z ≃ 6–7 LAEs (Nagao et al. 2005; Kashikawa et al. 2012; Zabl et al. 2015), spatially extended Lyα blobs (LABs: Dey et al. 2005; Prescott et al. 2009, 2013; Arrigoni Battaia et al. 2015), z ≃ 2–3 metal-poor and star-forming galaxies (Shapley et al. 2003; Erb et al. 2010), AGNs, QSOs, and radio galaxies (Heckman et al. 1991; Villar-Martín et al. 2007; Humphrey et al. 2013; Borisova et al. 2016).5 We add CR7 with our updated He ii/Lyα constraint in subsection 4.5. The UV-nebular lines of C iv, He ii, and O iii] are not detected from all of our seven bright LAEs, even for CR7, except for a tentative C iv detection (subsection 5.3). Albeit with only upper limits on the line flux ratios, we find that our bright LAEs typically have flux ratios of He ii/Lyα and C iv/Lyα lower than those of AGNs, QSOs, radio galaxies, and LABs, but similar to those of star-forming galaxies in Shapley et al. (2003) and Erb et al. (2010). Interestingly, the UV-nebular lines are extremely faint for several of our bright LAEs. For such objects, the flux ratio of the UV-nebular lines relative to Lyα, i.e., fUV line/fLyα, is below the order of 1%. Fig. 9. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/Lyα vs. C iv/Lyα. The red filled squares indicate our bright LAEs. The red cross denotes our bright LAE whose C iv emission line is tentatively detected (see subsection 5.3). The red open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The green arrow and dashed line are our He ii/Lyα constraint for CR7 (see subsection 4.5). The green filled symbols represent LABs (green filled square: Dey et al. 2005; green filled pentagons: Prescott et al. 2009, 2013; green filled diamonds: Arrigoni Battaia et al. 2015). The cyan filled symbols represent z ≃ 2–3 star-forming galaxies (cyan filled inverse triangle: Shapley et al. 2003; cyan filled circle Erb et al. 2010). The black and yellow symbols indicate AGNs, QSOs, and radio galaxies (black crosses: Villar-Martín et al. 2007; black filled triangles: Heckman et al. 1991; yellow filled triangles: Humphrey et al. 2013; black filled circles: Borisova et al. 2016). The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 9. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/Lyα vs. C iv/Lyα. The red filled squares indicate our bright LAEs. The red cross denotes our bright LAE whose C iv emission line is tentatively detected (see subsection 5.3). The red open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The green arrow and dashed line are our He ii/Lyα constraint for CR7 (see subsection 4.5). The green filled symbols represent LABs (green filled square: Dey et al. 2005; green filled pentagons: Prescott et al. 2009, 2013; green filled diamonds: Arrigoni Battaia et al. 2015). The cyan filled symbols represent z ≃ 2–3 star-forming galaxies (cyan filled inverse triangle: Shapley et al. 2003; cyan filled circle Erb et al. 2010). The black and yellow symbols indicate AGNs, QSOs, and radio galaxies (black crosses: Villar-Martín et al. 2007; black filled triangles: Heckman et al. 1991; yellow filled triangles: Humphrey et al. 2013; black filled circles: Borisova et al. 2016). The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) 5 Discussion 5.1 Properties of bright LAEs at z ≃ 6 We summarize the properties of the bright z ≃ 6–7 LAEs which have been revealed in our statistical study (section 4): The Lyα equivalent widths, EW0,Lyα, range from ∼10 Å to ∼300 Å. The Lyα line widths are ∼200–400 km s−1. There are no detections of X-ray, MIR, or radio emission. The N v emission line is not detected down to an N v/Lyα flux ratio of ∼10%. Most of the bright LAEs have compact Lyα emission. Only 5 objects out of the 28 bright LAEs show Lyα emission that is significantly extended compared to the point spread function FWHM size of ∼ 0$${^{\prime\prime}_{.}}$$7 in the ground-based HSC NB images. The UV-nebular lines of C iv, He ii, and O iii] are not detected from any of our seven bright LAEs, even for CR7, except for a tentative C iv detection (subsection 5.3). The flux ratio of the UV-nebular lines relative to Lyα is fUV line/fLyα ≲ 1%–10%. Here we discuss the physical origins of bright LAEs with log LLyα/[erg s−1] ≃ 43–44. The bright Lyα emission could be reproduced by several mechanisms: (1) gas photoionization by a hidden AGN, (2) strong UV radiation from Pop III stellar populations, (3) gas shock heating by strong outflows from central galaxies, and (4) intense starbursts by galaxy mergers. First, we discuss the possibility of AGNs. For z ≃ 2, Konno et al. (2016) have identified a significant excess of LAE number density at the Lyα LF bright end of log LLyα/[erg s−1] ≳ 43.4. All of the z ≃ 2 LAEs in the bright-end excess are detected in X-ray, UV, or radio data, suggesting that the bright Lyα emission is produced by central AGN activity. Similarly, there is a possibility that AGNs enhance the Lyα luminosity for bright LAEs at z ≃ 6–7. However, we find no clear signatures of AGNs according to the narrow Lyα line widths of ≲400 km s−1, and no detections of the N v line, X-ray, MIR, or radio emission. Thus, the bright LAEs at z ≃ 5.7–6.6 do not host broad-line AGNs, regardless of the bright Lyα emission. Secondly, we discuss the possibility of Pop III stellar populations. There is a possibility that strong UV radiation from Pop III stellar populations enhance the Lyα luminosity (e.g., Schaerer 2002). In our deep NIR spectroscopy, we find that there are no detections of the He ii emission line from CR7, Himiko, or our seven bright LAEs which are observed with NIR spectrographs. Moreover, the Lyα EW does not significantly exceed the EW0,Lyα value of 240 Å for the bright LAEs. No He ii detection and the small EW0,Lyα values might indicate that the bright LAEs do not host Pop III stellar populations. No Pop III stellar populations in bright LAEs might be supported by theoretical studies. According to a recent theoretical study of Yajima and Khochfar (2017), Pop III-dominated galaxies at z ≃ 7 have a Lyα luminosity of LLyα ≃ 3.0 × 1042–2.1 × 1043 erg s−1, which is slightly lower than that of our bright LAEs. However, we cannot reach the conclusion that Pop III stellar populations exist in bright LAEs from the current data of He ii measurements. The detectability of the He ii emission line would largely depend on the stellar initial mass function of galaxies (see subsection 5.4). To examine whether bright LAEs host Pop III stellar populations, we require NIR spectra whose depth is ∼10 × deeper than the current NIR flux limits. Thirdly, we discuss the possibility that strong outflows enhance the Lyα luminosity (e.g., Dijkstra & Wyithe 2010). If strong outflows exist, expelling high-velocity clouds could make Lyα lines broad and Lyα emission spatially extended. Our spectroscopy reveals that bright LAEs have a narrow Lyα emission line of ΔVFWHM ≲ 400 km s−1. Our Aiso measurements also indicate that most of our bright LAEs show spatially compact Lyα emission (see subsection 4.1 and table 6). The narrow Lyα line width and the spatially compact Lyα emission might suggest no strong gaseous outflow from the bright LAEs. However, we cannot conclude the presence of gaseous outflow based on our current data of optical spectra and NB images due to the resonance nature of Lyα photons. To investigate the presence of gaseous outflow, we have to directly measure velocity shifts of low-ionization metal lines with deep NIR spectra for the rest-frame UV continuum emission (e.g., Shibuya et al. 2014a; Erb et al. 2014, 2015; Trainor et al. 2015; Sugahara et al. 2017). Finally, we discuss the possibility that intense starbursts driven by galaxy mergers produce the large Lyα luminosity. High spatial resolution imaging observations with Hubble WFC3 have been conducted for two objects out of the 28 bright LAEs, Himiko and CR7, both of which show multiple subcomponents in the rest-frame UV continuum emission (Ouchi et al. 2013; Sobral et al. 2015). These multiple subcomponents could be indicative of galaxy mergers (e.g., Jiang et al. 2013; Shibuya et al. 2014b; Kobayashi et al. 2016). However, the galaxy morphology has been unclear for the other 26 bright LAEs in the ground-based and seeing-limited HSC images. In summary, the physical origins of bright LAEs are still unknown. At least we can conclude that the bright Lyα emission does not originate from broad-line AGNs. To obtain a definitive conclusion, we need to systematically perform deep NIR spectroscopy and high spatial resolution imaging observations for a large number of bright LAEs. 5.2 Relation between UV-nebular line EW and UV-continuum luminosity Combining samples of our bright LAEs and faint dropouts at z ≃ 5–7, we examine the relation between the UV-nebular line EWs of C iv, He ii, and O iii] and UV-continuum luminosity. Figure 10 presents the rest-frame EW of C iv, He ii, and O iii] as a function of MUV for our bright LAEs and dropouts in the literature (e.g., Stark et al. 2015; Mainali et al. 2017; Smit et al. 2017). Here we plot four UV continuum-detected objects out of our seven bright LAEs whose UV-nebular line EW can be constrained. The EW upper limits of our bright LAEs are typically ≲2.3, 4.0, and 2.9 Å for C iv, He ii, and O iii] lines, respectively. On the other hand, faint dropouts with MUV ≳ −20 strongly emit C iv and O iii] lines with $$EW_{\rm 0,C\,{\scriptscriptstyle IV}}\simeq 20$$–40 Å and $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}\simeq 5$$–10 Å, respectively. Fig. 10. View largeDownload slide Line equivalent widths of C iv (top), He ii (middle), and O iii] (bottom) as a function of UV magnitude, MUV. The red filled squares denote our four bright LAEs with an upper limit of UV-nebular line EW. The red cross represents the LAEs whose C iv emission is tentatively detected. The cyan filled symbols denote high-z dropout galaxies (cyan filled circles: z ≃ 7 dropouts in Stark et al. 2015; cyan filled diamond: z ≃ 6 dropout in Mainali et al. 2017; cyan filled triangle: Smit et al. 2017). The gray symbols indicate z ≃ 2–3 galaxies (gray crosses: Amorín et al. 2017; gray open inverse-triangle: Stark et al. 2014). The gray curves represent the best-fit quadratic functions to the data points of z ≃ 6–7 dropouts in Stark et al. 2014, Mainali et al. (2017), and our LAEs. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 10. View largeDownload slide Line equivalent widths of C iv (top), He ii (middle), and O iii] (bottom) as a function of UV magnitude, MUV. The red filled squares denote our four bright LAEs with an upper limit of UV-nebular line EW. The red cross represents the LAEs whose C iv emission is tentatively detected. The cyan filled symbols denote high-z dropout galaxies (cyan filled circles: z ≃ 7 dropouts in Stark et al. 2015; cyan filled diamond: z ≃ 6 dropout in Mainali et al. 2017; cyan filled triangle: Smit et al. 2017). The gray symbols indicate z ≃ 2–3 galaxies (gray crosses: Amorín et al. 2017; gray open inverse-triangle: Stark et al. 2014). The gray curves represent the best-fit quadratic functions to the data points of z ≃ 6–7 dropouts in Stark et al. 2014, Mainali et al. (2017), and our LAEs. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) As shown in figure 10, we find a trend that EWs of C iv and O iii] increase towards faint MUV. Such a trend is similar to recent study results for z ≃ 2–3 galaxies showing that UV-nebular lines are predominantly detected in faint sources (Stark et al. 2014; Amorín et al. 2017; see also Du et al. 2017 for C iii]λλ1907,1909). On the other hand, we do not find a clear trend for He ii due to no He ii detection from all of our bright LAEs or z ≃ 6–7 dropouts. For the clarity of the $$EW_{\rm 0,C\,{\scriptscriptstyle IV}}$$ and $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}$$ relations, we fit a quadratic function to the data points of z ≃ 6–7 dropouts in Stark et al. (2015), Mainali et al. (2017), and our LAEs. In the fit, we use the values of EW upper limits for the objects without a UV-nebular line detection. We exclude the LAE with a tentative C iv detection and a z ≃ 7 dropout with a weak $$EW_{\rm 0,O\,{\scriptscriptstyle III}]}$$ constraint in Stark et al. (2015) for the fit (see subsection 5.3). The best-fit quadratic functions are shown in figure 10. In contrast to the gravitationally lensed and faint dropouts of Stark et al. (2015), Mainali et al. (2017), and Smit et al. (2017), our bright LAEs have a moderately bright UV magnitude ranging from MUV ≃ −20 to ≃ −22. No UV-nebular line detections from the bright sources could suggest that such a high EW0 value is a characteristic of low-mass galaxies. The high UV-nebular line EW in low-mass galaxies would be due to a hard ionizing spectrum (i.e., ξion, the number of LyC photons per UV luminosity; e.g., Nakajima et al. 2016; Bouwens et al. 2016). Moreover, recent studies for z ≃ 0 galaxies report that high-ionization UV-nebular lines highly depend on the gas-phase metallicity (e.g., Senchyna et al. 2017). Our possible EW–MUV correlation may also suggest a dependence of the UV-nebular line EW on metallicity for z ≃ 6–7 galaxies via the mass–metallicity relation. 5.3 A tentative detection of the C iv emission line In this section, we discuss the EW and UV-nebular line ratios for the LAE whose C iv is tentatively detected (subsection 4.4). We estimate the C iv EW, $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$, by using the upper limits of the rest-frame UV continuum flux density. We obtain $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}\gtrsim 40$$ Å, which is comparable to that of a z ≃ 7 dropout in Stark et al. (2015). The $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$ value might be too high according to the anti-correlation between EW and UV-continuum luminosity in subsection 5.2. However, it should be noted that the UV continuum is not detected for HSC J233408+004403. In the case that the UV magnitude is fainter than MUV ≃ −21, the $$EW_{\rm 0, C\,{\scriptscriptstyle IV}}$$ value would be comparable to the trend that EW0 is high at a high UV-continuum luminosity. Assuming that the C iv emission line is detected in HSC J233408+004403, we compare the He ii/C iv and O iii]/C iv line flux ratios of HSC J233408+004403 with those of star-forming galaxies at z ≃ 0–7 and AGNs/QSOs (Hainline et al. 2011; Alexandroff et al. 2013; Stark et al. 2014; Berg et al. 2016; Vanzella et al. 2016, 2017; Mainali et al. 2017). Figure 11 shows the line flux ratios of He ii/C iv and O iii]/C iv for HSC J233408+004403 and star-forming galaxies and AGNs/QSOs. As shown in figure 11, HSC J233408+004403 has a flux ratio limit of log(He ii/C iv) ≲ −0.9, similar to that of star-forming galaxies at z ≃ 7. Fig. 11. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/C iv vs. O iii]/C iv. The red cross denotes our bright LAE with a tentative C iv emission, HSC J233408+004403. The cyan filled symbols indicate dropouts at z ≃ 2–7 (cyan squares: Vanzella et al. 2017; cyan filled inverse-triangle: Vanzella et al. 2016; cyan filled diamond: Mainali et al. 2017; cyan filled triangle: Stark et al. 2014). The green asterisks represent z ≃ 0 galaxies in Berg et al. (2016). The crosses represent QSOs and AGNs (black crosses: z ≃ 2–4 type-II QSOs in Alexandroff et al. 2013; magenta cross: z ≃ 2–3 AGN composite in Hainline et al. 2011). The blue and red arrows indicate the star-forming galaxy and AGN regions predicted by a photoionization model of Feltre, Charlot, and Gutkin (2016), respectively. (Color online) Fig. 11. View largeDownload slide Flux ratios of UV-nebular emission lines, He ii/C iv vs. O iii]/C iv. The red cross denotes our bright LAE with a tentative C iv emission, HSC J233408+004403. The cyan filled symbols indicate dropouts at z ≃ 2–7 (cyan squares: Vanzella et al. 2017; cyan filled inverse-triangle: Vanzella et al. 2016; cyan filled diamond: Mainali et al. 2017; cyan filled triangle: Stark et al. 2014). The green asterisks represent z ≃ 0 galaxies in Berg et al. (2016). The crosses represent QSOs and AGNs (black crosses: z ≃ 2–4 type-II QSOs in Alexandroff et al. 2013; magenta cross: z ≃ 2–3 AGN composite in Hainline et al. 2011). The blue and red arrows indicate the star-forming galaxy and AGN regions predicted by a photoionization model of Feltre, Charlot, and Gutkin (2016), respectively. (Color online) We compare the limits of flux ratios with those of photoionization models of star-forming galaxies and AGNs in Feltre, Charlot, and Gutkin (2016). The comparison suggests that the constraints on the line flux ratios for HSC J233408+004403 are more comparable to star-forming galaxies as ionizing sources than AGNs predicted by the model, supporting the results of no clear signatures of AGN activity in subsections 4.2 and 4.3. 5.4 Spectral hardness of bright LAEs We investigate the spectral hardness of bright LAEs at z ≃ 6–7 based on the upper limits on the He ii/Lyα line flux ratios (subsection 4.4). Figure 12 shows the spectral hardness, QHe +/QH, as a function of metallicity, Z, for our bright LAEs and z ≃ 6–7 LAEs in previous studies (Himiko in Zabl et al. 2015; SDF-LEW-1 in Kashikawa et al. 2012; SDF J132440.6+273607 in Nagao et al. 2005). Here we use QHe +/QH, which is more model independent than physical quantities of, e.g., ξion. The QHe +/QH value is calculated with   \begin{equation} \frac{f_{\rm He}}{f_{\rm Ly\alpha }} \simeq 0.55 \times \frac{Q({\rm He}^+)}{Q({\rm H})}, \end{equation} (1)where fHe and fLyα are the flux of the He ii and Lyα emission lines, respectively, and Q(He+) and Q(H) are the emitted number of hydrogen and helium ionizing photons, respectively. QHe +/QH traces the energy range between 54.4 and 13.6 eV. The factor of 0.55 depends on the electron temperature, here taken to be Te = 30 kK (Schaerer 2002). The Q(He+)/Q(H) upper limits calculated from the He ii/Lyα line flux ratios (table 7) ranges from log Q(He+)/Q(H) ≃ −0.5 to ∼−1.8. For five objects of our bright LAEs, we put strong upper limits of log Q(He+)/Q(H) ≲ −1.8. Fig. 12. View largeDownload slide Spectral hardness of the He+ ionizing flux, $$Q_{\rm He^+}/Q_{\rm H}$$, as a function of metallicity. The red filled circles represent our bright LAEs. The magenta line indicates the strongest upper limit of our $$Q_{\rm He^+}/Q_{\rm H}$$ estimates. The filled red squares, blue circles, and green triangles with colored lines denote the model predictions of Schaerer (2003) for stellar initial mass functions with mass ranges of 1–100 M⊙ , 1–500 M⊙ , and 50–500 M⊙ , respectively. The open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The open green pentagon is $$Q_{\rm He^+}/Q_{\rm H}$$ obtained from our He ii/Lyα constraint for CR7 (see subsection 4.5). The metallicity of the observational data points is arbitrary. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Fig. 12. View largeDownload slide Spectral hardness of the He+ ionizing flux, $$Q_{\rm He^+}/Q_{\rm H}$$, as a function of metallicity. The red filled circles represent our bright LAEs. The magenta line indicates the strongest upper limit of our $$Q_{\rm He^+}/Q_{\rm H}$$ estimates. The filled red squares, blue circles, and green triangles with colored lines denote the model predictions of Schaerer (2003) for stellar initial mass functions with mass ranges of 1–100 M⊙ , 1–500 M⊙ , and 50–500 M⊙ , respectively. The open symbols indicate z ≳ 6 LAEs (red open square: Himiko in Zabl et al. 2015; red open circle: SDF-LEW-1 in Kashikawa et al. 2012; red open triangle: SDF J132440.6+273607, Nagao et al. 2005). The open green pentagon is $$Q_{\rm He^+}/Q_{\rm H}$$ obtained from our He ii/Lyα constraint for CR7 (see subsection 4.5). The metallicity of the observational data points is arbitrary. The data points without a UV-nebular line detection indicate 2 σ upper limits. (Color online) Figure 12 also shows the model spectral hardness predicted from initial mass functions (IMFs) with different stellar mass ranges of M* = 1–100 M⊙ , 1–500 M⊙ , and M* = 50–500 M⊙ (Schaerer 2003). The metallicity of bright LAEs has not been constrained yet. If we assume that bright LAEs are extremely metal poor below log Z ≃ −8, top-heavy IMFs with M* = 50–500 M⊙ might be ruled out by our QHe +/QH constraints for z ≃ 6–7 LAEs. 6 Summary and conclusions We present Lyα and UV-nebular emission line properties of bright LAEs at z = 6–7 with a luminosity of log LLyα/[erg s−1] = 43–44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru/HSC survey data (Ouchi et al. 2018; Shibuya et al. 2018). Our findings are summarized as follows: Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 97 LAEs at z = 6–7 in SILVERRUSH. Our observations enlarge a spectroscopic sample of bright LAEs by a factor of four, allowing for a statistical study on bright LAEs. We find that all the bright LAEs have a narrow Lyα line width of ≲400 km s−1, and do not have X-ray, MIR, radio, or N v λλ1238,1240 emissions regardless of the large Lyα luminosity. The narrow Lyα line widths and no X-ray, MIR, radio, or N v detections suggest that the bright LAEs are not broad-line AGNs. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS NIR spectroscopy, reaching the 3 σ flux limit of ∼2 × 10−18 erg s−1 for the UV-nebular emission lines of He ii λ1640, C iv λλ1548,1550, and O iii]λλ1661,1666. Except for one tentative detection of C iv, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of EW0 of ∼2.3, 4.0, and 2.9 Å for He ii, C iv, and O iii] lines, respectively. We investigate the VLT/X-SHOOTER spectrum of CR7, for which 6 σ detection of He ii is claimed by Sobral et al. (2015). Although two of the authors of this paper and the ESO-archive service carefully reanalyzed the X-SHOOTER data used in the study of Sobral et al. (2015), no He ii signal for CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. Spectral properties of these bright LAEs are clearly different from those of faint dropouts at z ∼ 7 that have strong UV-nebular lines, as shown in the various studies (e.g., Stark et al. 2015). Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and UV-continuum luminosity, which are similar to those found at z ≃ 2–3. The high spatial resolution imaging and deep spectroscopic observations with the Hubble Space Telescope and James Webb Space Telescope will reveal the morphology, ISM properties, and the origins of bright LAEs. Acknowledgements We would like to thank Masayuki Akiyama, Mark Dijkstra, Richard Ellis, Tadayuki Kodama, Jorryt Matthee, David Sobral, Daniel Stark, Yuma Sugahara, and Zheng Zheng for useful discussion and comments. We also thank Kentaro Aoki and Ichi Tanaka for their support of the FOCAS and MOIRCS observations. We thank the anonymous referee for constructive comments and suggestions. This work is based on observations taken by the Subaru Telescope and the Keck telescope, which are operated by the National Observatory of Japan. This work was supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, KAKENHI (15H02064), (23244025), and (21244013) Grant-in-Aid for Scientific Research (A) through Japan Society for the Promotion of Science (JSPS), and an Advanced Leading Graduate Course for Photon Science grant. NK is supported by JSPS grant 15H03645. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), the Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at ⟨http://dm.lsst.org⟩. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. Appendix. Spectroscopically confirmed LAEs with NB > 24 Tables 8 and 9 present faint NB > 24 spectroscopically confirmed HSC LAEs at z ≃ 6.6 and z ≃ 5.7, respectively. See sub-subsection 3.1.4 for more details. Footnotes † Based on data obtained with the Subaru Telescope. The Subaru Telescope is operated by the National Astronomical Observatory of Japan. ‡ This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. 1 ⟨http://cos.icrr.u-tokyo.ac.jp/rush.html⟩. 2 ⟨http://iraf.noao.edu/⟩. 3 ⟨https://keck-datareductionpipelines.github.io/MosfireDRP/⟩. 4 Recently, the He ii/Lyα line flux ratio for CR7 has been updated based on the flux recalibration of the X-SHOOTER spectrum in Matthee et al. (2017) and D. Sobral (in preparation). 5 Note that the C iv doublet is not spectroscopically resolved for some of the previous studies. The flux upper limit for such an unresolved C iv doublet would be higher than that of resolved C iv lines. 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