Monthly Notices of the Royal Astronomical Society

Singh, Sukhdeep; Shakir, Ali; Jagvaral, Yesukhei; Mandelbaum, Rachel

doi: 10.1093/mnras/stae1034pmid: N/A

ABSTRACTIt has long been known that galaxy shapes align coherently with the large-scale density field. Characterizing this effect is essential to interpreting measurements of weak gravitational lensing, the deflection of light from distant galaxies by matter overdensities along the line of sight, as it also produces coherent galaxy alignments that we wish to interpret in terms of a cosmological model. Existing direct measurements of intrinsic alignments using galaxy samples with high-quality shape and redshift measurements typically use well-understood but sub-optimal projected estimators, which do not make good use of the information in the data when comparing those estimators to theoretical models. We demonstrate a more optimal estimator, based on a multipole expansion of the correlation functions or power spectra, for direct measurements of galaxy intrinsic alignments. We show that even using the lowest order multipole alone increases the significance of inferred model parameters using simulated and real data, without any additional modelling complexity. We apply this estimator to measurements of parameters of the non-linear alignment model using data from the Sloan Digital Sky survey, demonstrating consistent results with a factor of ∼2 greater precision in parameter fits to intrinsic alignments models. This result is functionally equivalent to quadrupling the survey area, but without the attendant costs – thereby demonstrating the value in using this new estimator in current and future intrinsic alignments measurements using spectroscopic galaxy samples.

Zheng, Zhiyuan; Shi, Yong; Jin, Shuowen; Dannerbauer, H; Gu, Qiusheng; Li, Xin; Yu, Xiaoling

doi: 10.1093/mnras/stae1036pmid: N/A

ABSTRACTActive galactic nuclei (AGNs) are known to exhibit optical/ultraviolet variability and most of them can be well modelled by the damped random walks. Physical processes that are not related to the accretion disc, such as tidal disruption events (TDEs) or moving foreground dusty clouds, can cause flare-like and eclipse-like features in the optical light curve. Both long-term and high-cadence monitoring are needed to identify such features. By combining the Sloan Digital Sky Survey (SDSS), Panoramic Survey Telescope and Rapid Response System, and the Zwicky Transient Facility (ZTF) survey, we are able to identify a rare sample (11) out of the SDSS quasar catalogue ($\sim\!\! 83\, 000$). These quasars exhibit more or less constant brightness but show rapid optical variation in the epochs of ZTF Public Data Release 2. To investigate the possible origins of these flare/eclipse-like variabilities, we propose the second-epoch spectroscopic observations with the Gran Telescopio CANARIAS. We find that the change in accretion rate plays a significant role in these quasar variabilities. Among them, we identify two changing-look AGN candidates: SDSS J1427+2930 and SDSS J1420+3757. The luminosity change of the former may be caused by the enhanced supermassive black hole’s accretion or the TDE, while the latter is more related to the change in the accretion rate.

Zhu, Li-Tao; Li, Jie; Wang, Zhongxiang; Zhang, Ju-Jia

doi: 10.1093/mnras/stae1044pmid: N/A

ABSTRACTWe report the finding of four changing look (CL) Active Galactic Nuclei (AGN). We selected these sources due to their potential as interesting targets when considering their relatively large optical flux variations and related mid-infrared flux variations. To identify their CL feature, we use archival spectra from the Sloan Digital Sky Survey (SDSS) taken at least 8 yr ago as well as spectra taken recently from the Transient Name Server (TNS) and with the 2.4-m LiJiang telescope (LJT). We study the sources’ spectral changes by fitting and determining the Hα and Hβ components and verify their CL behaviour. When comparing the TNS and/or LJT spectra to the SDSS ones, all four sources showed the appearance of a broad or a stronger broad Hα component and a relatively weak broad Hβ component. As two of the four sources are established to have a brighter-and-bluer feature in the photometric data, during the time periods in which the TNS and LJT spectra were taken, this feature likely accompanied the turn-on of the broad components. Thus, we suggest that this brighter-and-bluer feature can be used as a criterion for efficiently finding CL sources among previously spectroscopically classified type 2 AGN, such as from among the sources provided by the SDSS.

Lloyd, Sheridan J; Chadwick, Paula M; Brown, Anthony M

doi: 10.1093/mnras/stae1058pmid: N/A

ABSTRACTWe analyse 13 yr of Fermi Large Area Telescope Pass 8 events from 127 gamma-ray emitting millisecond pulsars (MSPs) in the energy range 0.1–100 GeV and significantly detect 118 MSPs. We fit the stacked emission with a log parabola (LP) spectral model that we show is preferred to two previously published models. We consider the influence of pulsar properties and observed geometric effects on spectral features by defining energy flux colours for both the individual MSPs, and our stacked model as a baseline. There is no correlation of colours with pulsar luminosity, $\dot{E}$, surface magnetic field, or magnetic impact angle. We also find that pulsar geometry has little effect on the observed gamma-ray spectrum, which is in tension with previous modelling of gamma-ray emission with respect to pulsar geometry. Our LP MSP model is applicable to problems where an ensemble of gamma-ray MSPs is considered, such as that of the Galactic Centre excess or in the case of emission from globular clusters.

Slíz-Balogh, Judit; Mádai, Attila; Sári, Pál; Barta, András; Horváth, Gábor

doi: 10.1093/mnras/stae1062pmid: N/A

ABSTRACTThe Kordylewski dust clouds (KDCs) around the L5 and L4 Lagrange points of the Earth–Moon system have been first observed by imaging polarimetry in 2017 and 2022 in a Hungarian astronomical observatory. Due to the non-ideal (almost always hazy, aerosol-polluted) astroclimate of Hungary and the extremely low intensity of dust-scattered sunlight, the polarimetric hunt after both KDCs lasted 2–7 yr. Waiting for cloud- and aerosol-free atmosphere and appropriate astronomical conditions (e.g. moonless sky with above-horizon KDC) in our Hungarian observatory takes a long time. Thus, our goal was to build a portable imaging polarimetric, wide field-of-view telescope and use it in the very good astroclimate of the Isabis Astro Lodge in the Khomas Highland of Namibia. Our long term aim is to study the dynamics of KDCs with this instrument in Namibian 1-month astropolarimetric campaigns in the next decade. In this work, we describe our portable imaging polarimetric telescope and present our first KDC observation achieved with it in Namibia during our 4-week astropolarimetric campaign between 2023 July 18 and August 15. We conclude that our portable polarimetric telescope functions well. Using it in Namibia, we corroborated the existence of the L5 KDC, the polarization characteristics (polarization degree and angle) of which refer to an inhomogeneous dust cloud composed of several particle agglomerations that scatter and linearly polarize the illuminating sunlight.

, ; , ; , ; , ; Guo, Hengxiao

doi: 10.1093/mnras/stae1063pmid: N/A

ABSTRACTNGC 4395 is a dwarf type 1 Seyfert galaxy with a possible intermediate-mass black hole of several $\rm {10^4}$ solar masses in its centre. As a well-studied object, its broad-line region size has been measured via H $\rm {\alpha }$ time lag in numerous spectroscopic reverberation mapping (SRM) and narrow-band photometric reverberation mapping (PRM) campaigns. Here, we present its H $\rm {\alpha }$ time lag measurement using broad-band photometric data, with the application of our newly developed ICCF-Cut (Interpolation and Cross-Correlation Function - Cut) method as well as the javelin (Just Another Vehicle for Estimating Lags In Nuclei) and χ2 methods. Utilizing the minute-cadence multiband light curves obtained from the $\rm {2}$-m Faulkes Telescope North and $\rm {10.4}$-m Gran Telescopio Canarias telescopes in recent works, we measured its H $\rm {\alpha }$ lag as approximately 40–90 min from broad-band PRM. With the H $\rm {\alpha }$ emission line velocity dispersion, we calculated its central black hole mass as $M_{\rm BH} = (8\pm 4) \times 10^3\ \mathrm{ M}_{\rm \odot }$. These results are comparable with previous results obtained by narrow-band PRM and SRM, providing further support to an intermediate-mass black hole in NGC 4395. In addition, our study also validates the ICCF-Cut as an effective method for broad-band PRM, which holds the potential for widespread application in the era of large multi-epoch, high-cadence photometric surveys.

Chen, Xiao; Ding, Yuanze; Wang, Wei; Nishimura, Osamu; Liu, Qi; Zhang, Shuang-Nan; Ge, Mingyu; Lu, Fangjun; Qu, Jinlu; Song, Liming; Zhang, Shu

doi: 10.1093/mnras/stae1071pmid: N/A

ABSTRACTCyclotron resonant scattering features (CRSFs) are the absorption features in the X-ray spectra of strongly magnetized accretion neutron stars (NSs), which are probably the most reliable probe to the surface magnetic fields of NSs. The high-mass X-ray binary GX 301–2 exhibits a very wide, variable, and complicated CRSF in the average spectra, which should be two absorption lines based on Nuclear Spectroscopic Telescope Array (NuStar) and Hard X-ray Modulation Telescope (Insight-HXMT) observations. With the Insight-HXMT frequent observations, we performed the phase-resolved spectroscopy and confirmed two cyclotron absorption lines in the phase-resolved spectra, with their centroid energy ratio ∼1.6–1.7 in the supercritical luminosity case. A major hindrance in understanding those CRSFs is the very poorly constrained magnetic inclination angle, which is also a fundamental property of an NS and key to understanding the emission characteristics of a pulsar. Comparing the phase-resolved CRSF with simulated X-ray spectra, the magnetic inclination angle is found to be ≳70°, i.e. nearly orthogonal between the NS’s spin and magnetic axis. The implications of an orthogonal rotator and magnetic structure evolution in the accreting X-ray binary are also discussed.

Mustill, Alexander J; Davies, Melvyn B; Kenworthy, Matthew A

doi: 10.1093/mnras/stae1074pmid: N/A

ABSTRACTSeveral stars show deep transits consistent with discs of roughly $1\mathrm{\, R}_\odot$ seen at moderate inclinations, likely surrounding planets on eccentric orbits. We show that this configuration arises naturally as a result of planet–planet scattering when the planets possess satellite systems. Planet–planet scattering explains the orbital eccentricities of the discs’ host bodies, while the close encounters during scattering lead to the exchange of satellites between planets and/or their destabilization. This leads to collisions between satellites and their tidal disruption close to the planet. Both of these events lead to large quantities of debris being produced, which in time will settle into a disc such as those observed. The mass of debris required is comparable to a Ceres-sized satellite. Through N-body simulations of planets with clones of the Galilean satellite system undergoing scattering, we show that 90 per cent of planets undergoing scattering will possess debris from satellite destruction. Extrapolating to smaller numbers of satellites suggests that tens of per cent of such planets should still possess circumplanetary debris discs. The debris trails arising from these events are often tilted at tens of degrees to the planetary orbit, consistent with the inclinations of the observed discs. Disruption of satellite systems during scattering thus simultaneously explains the existence of debris, the tilt of the discs, and the eccentricity of the planets they orbit.

Rodríguez Montero, Francisco; Martin-Alvarez, Sergio; Slyz, Adrianne; Devriendt, Julien; Dubois, Yohan; Sijacki, Debora

doi: 10.1093/mnras/stae1083pmid: N/A

ABSTRACTDuring the last decade, cosmological simulations have managed to reproduce realistic and morphologically diverse galaxies, spanning the Hubble sequence. Central to this success was a phenomenological calibration of the few included feedback processes, while glossing over higher complexity baryonic physics. This approach diminishes the predictive power of such simulations, preventing to further our understanding of galaxy formation. To tackle this fundamental issue, we investigate the impact of cosmic rays (CRs) and magnetic fields on the interstellar medium and the launching of outflows in a cosmological zoom-in simulation of a Milky Way-like galaxy. We find that including CRs decreases the stellar mass of the galaxy by a factor of 10 at high redshift and ∼4 at cosmic noon, leading to a stellar mass to halo mass ratio in good agreement with abundance matching models. Such decrease is caused by two effects: (i) a reduction of cold, high-density, star-forming gas, and (ii) a larger fraction of supernova (SN) events exploding at lower densities, where they have a higher impact. SN-injected CRs produce enhanced, multiphase galactic outflows, which are accelerated by CR pressure gradients in the circumgalactic medium of the galaxy. While the mass budget of these outflows is dominated by the warm ionized gas, warm neutral and cold gas phases contribute significantly at high redshifts. Importantly, our work shows that future JWST observations of galaxies and their multiphase outflows across cosmic time have the ability to constrain the role of CRs in regulating star formation.

Feng, Xin-Ming; Yang, Yuan-Pei; Li, Qiao-Chu

doi: 10.1093/mnras/stae1092pmid: N/A

ABSTRACTFast radio bursts (FRBs) are cosmological radio transients with millisecond durations and extremely high brightness temperatures. One FRB repeater, FRB 180916.J0158+65 (FRB 180916B), was confirmed to appear 16.35-day periodic activities with 5-day activity window. Another FRB repeater, FRB 121102, and two soft gamma-ray repeaters (SGRs), SGR 1935+2154 and SGR 1806−20, also show possible periodic activities. These periodicities might originate from the precession process of young magnetars due to the anisotropic pressure from the inner magnetic fields as proposed in the literature. In this work, we analyse a self-consistent model for the rotation evolution of magnetars and obtain the evolutions of magnetar precession and obliquity. We find that if the FRB repeaters and the SGRs with (possible) periodic activities originate from the magnetar precession, their ages would be constrained to be hundreds to tens of thousands of years, which is consistent with the typical ages of magnetars. Assuming that the FRB emission is beaming in the magnetosphere as proposed in the literature, we calculate the evolution of the observable probability and the duty cycle of the active window period. We find that for a given magnetar the observable probability increases with the magnetar age in the early stage and decreases with the magnetar age in the later stage; meanwhile, there are one or two active windows in one precession period if the emission is not perfectly axisymmetric with respect to the deformation axis of a magnetar, which could be tested by the future observation for repeating FRB sources.