Monthly Notices of the Royal Astronomical Society

Chen(陈千惠), Qian-Hui; Grasha, Kathryn; Battisti, Andrew J; Kewley, Lisa J; Madore, Barry F; Seibert, Mark; Rich, Jeff A; Beaton, Rachael L

doi: 10.1093/mnras/stac3790pmid: N/A

ABSTRACTBars play an important role in mixing material in the inner regions of galaxies and stimulating radial migration. Previous observations have found evidence for the impact of a bar on metallicity gradients but the effect is still inconclusive. We use the TYPHOON/PrISM survey to investigate the metallicity gradients along and beyond the bar region across the entire star-forming disc of five nearby galaxies. Using emission line diagrams to identify star-forming spaxels, we recover the global metallicity gradients ranging from −0.0162 to −0.073 dex kpc−1 with evidence that the galactic bars act as an agent in affecting in situ star formation as well as the motions of gas and stars. We observe cases with a ‘shallow-steep’ metallicity radial profile, with evidence of the bar flattening the metallicity gradients inside the bar region (NGC 5068 and NGC 1566) and also note instances where the bar appears to drive a steeper metallicity gradient producing ‘steep-shallow’ metallicity profiles (NGC 1365 and NGC 1744). For NGC 2835, a ‘steep-shallow’ metallicity gradient break occurs at a distance ∼4 times the bar radius, which is more likely driven by gas accretion to the outskirt of the galaxy instead of the bar. The variation of metallicity gradients around the bar region traces the fluctuations of star formation rate surface density in NGC 1365, NGC 1566, and NGC 1744. A larger sample combined with hydrodynamical simulations is required to further explore the diversity, and the relative importance of different ISM mixing mechanisms on the gas-phase metallicity gradients in local galaxies.

Rodríguez-González, A; Rivera-Ortiz, P R; Castellanos-Ramírez, A; Raga, A C; Hernández-Martínez, L; Cantó, J; Zapata, L A; Robles-Valdez, F

doi: 10.1093/mnras/stac3793pmid: N/A

ABSTRACTWe present reactive gasdynamic, axisymmetric simulations of dense, high-velocity clumps for modelling the CO streamers observed in Orion BN/KL. We have considered 15 chemical species, a cooling function for atomic and molecular gas, and heating through cosmic rays. Our numerical simulations explore different ejection velocities, interstellar medium density configurations, and CO content. Using the CO density and temperature, we have calculated the CO (J = 2 → 1) emissivity, and have built CO maps and spatially resolved line profiles, allowing us to see the CO emitting regions of the streamers and to obtain position velocity diagrams to compare with observations. We find that in order to reproduce the images and line profiles of the BN/KL CO streamers and H2 fingers, we need to have clumps that first travel within a dense cloud core, and then emerge into a lower-density environment.

Avdan, S; Akyuz, A; Acar, S; Akkaya Oralhan, I; Allak, S; Aksaker, N

doi: 10.1093/mnras/stac3811pmid: N/A

ABSTRACTWe investigated for a possible connection between the types of X-ray binaries (XRBs) and the properties of compact star clusters in the nearby galaxy NGC 628. Using Chandra archival data covering the years 2001–2018, 75 X-ray sources were detected within the field of view of observations. A total of 69 XRBs, one of which is an ultraluminous X-ray source (ULX), were found to be in the luminosity range of 3 × 1036 ≤ LX ≤ 2 × 1039 erg s−1. We identified the optical counterpart(s) of 15 of the 42 XRBs that coincide with the HST field of view via improved astrometry. We classified 15 of them as HMXBs based on the presence of the optical counterparts. The remaining sources with no optical counterparts were classified as LMXBs. We also search compact star clusters in this galaxy using the multiband optical images drawn from HST archives. 864 compact star clusters were identified and their ages and masses were determined by applying the best-fit SSP (Simple Stellar Population) model to their colour–colour diagram. We found that in NGC 628, HMXBs are associated with younger star clusters and LMXBs with older ones. Our findings support a connection between different types of XRBs and cluster ages, already known to exist for other galaxies.

Dhawan, Suhail; Borderies, Antonin; Macpherson, Hayley J; Heinesen, Asta

doi: 10.1093/mnras/stac3812pmid: N/A

ABSTRACTThe cosmological principle asserts that the Universe looks spatially homogeneous and isotropic on sufficiently large scales. Given its fundamental implications, it is important to empirically test its validity. In this paper, we use the Type Ia supernova (SN Ia) magnitude–redshift relation, from both the Pantheon and joint light-curve analysis compilations, to constrain theoretically motivated anisotropies in the Hubble flow. In particular, we constrain the quadrupole in the effective Hubble parameter and the dipole in the effective deceleration parameter. We find no significant quadrupole term regardless of the redshift frame used. Our results are consistent with the theoretical expectation of a quadrupole moment of a few percent at scales of ∼100 h−1 Mpc. We place an upper limit of an $\sim 10{{\%}}$ quadrupole amplitude relative to the monopole, H0, at these scales. We find that we can detect an $\sim 7{{\%}}$ quadrupole at the 5σ level, for a forecast low-z sample of 1055 SNe Ia. We find the signficance of an exponentially decaying dipole of the deceleration parameter depends on the redshift frame used. In the heliocentric frame, as expected, it is detected at ∼3σ significance. In the cosmic microwave background (CMB) rest frame, we find a marginal ∼2σ dipole, however, after applying peculiar velocity (PV) corrections, the dipole is insignificant. Finally, we find the best-fitting frame of rest relative to the supernovae to differ from that of the CMB at ∼2σ for both compilations, which reduces to <1σ when including PV covariance.

Banerjee, Arka; Abel, Tom

doi: 10.1093/mnras/stac3813pmid: N/A

ABSTRACTIn astronomy and cosmology significant effort is devoted to characterizing and understanding spatial cross-correlations between points – e.g galaxy positions, high energy neutrino arrival directions, X-ray and AGN sources, and continuous fields – e.g. weak lensing meiand Cosmic Microwave Background maps. Recently, we introduced the k-nearest neighbour (kNN) formalism to better characterize the clustering of discrete (point) data sets. Here, we extend it to the point – field cross-correlations analysis. It combines kNN measurements of the point data set with measurements of the field smoothed at many scales. The resulting statistics are sensitive to all orders in the joint clustering of the points and the field. We demonstrate that this approach, unlike the 2-pt cross-correlation, can measure the statistical dependence of two data sets even when there are no linear (Gaussian) correlations between them. We further demonstrate that this framework is far more effective than the two point function in detecting cross-correlations when the continuous field is contaminated by high levels of noise. For a particularly high level of noise, the cross-correlation between haloes and the underlying matter field in a cosmological simulation, between 10 h−1 Mpc and 30 h−1 Mpc, is detected at >5σ significance using the technique presented here, when the two-point cross-correlation significance is ∼1σ. Finally, we show that kNN cross-correlations of haloes and the matter field can be well modelled on quasi-linear scales using the Hybrid Effective Field Theory (HEFT) framework, with the same set of bias parameters as are used for 2-pt cross-correlations. The substantial improvement in the statistical power of detecting cross-correlations using this method makes it a promising tool for various cosmological applications.

Bera, Ankita; Samui, Saumyadip; Datta, Kanan K

doi: 10.1093/mnras/stac3814pmid: N/A

ABSTRACTIt is extremely important to understand the processes through which the thermal state of the inter-galactic medium (IGM) evolved in the early universe in order to study the evolution of HI 21-cm signal during cosmic dawn. Here, we consider the heating of the IGM due to cosmic ray (CR) protons generated by the supernovae from both early Pop III and Pop II stars. The low energy CR (cr protons from Pop III supernovae can escape from minihalos and heat the IGM via collision and ionization of hydrogen. Furthermore, high-energy protons generated in Pop II supernovae can escape the hosting halos and heat the IGM via magnetosonic Alfvén waves. We show that the heating due to these CR particles can significantly impact the IGM temperature and hence the global 21-cm signal at z ∼ 14−18. The depth, location, and duration of the 21-cm absorption profile are highly dependent on the efficiencies of CR heating. In particular, the Experiment to Detect the Epoch of Reionization Signature signal can be well fitted by the CR heating along with the Lyman-α coupling and the dark matter--baryon interaction that we consider to achieve a ‘colder IGM background’. Further, we argue that the properties of CRs and the nature of first generation of stars could be constrained by accurately measuring the global 21-cm absorption signal during the cosmic dawn.

Shobhana, Devika; Norris, Ray P; Filipović, Miroslav D; Barnes, Luke A; Hopkins, Andrew M; Prandoni, Isabella; Brown, Michael J I; Shabala, Stanislav S

doi: 10.1093/mnras/stac3319pmid: N/A

ABSTRACTUsing the Lyman Dropout technique, we identify 148 candidate radio sources at z ≳ 4–7 from the 887.5 MHz Australian Square Kilometre Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112 radio sources are currently known beyond redshift z ∼ 4. However, simulations predict that hundreds of thousands of radio sources exist in that redshift range, many of which are probably in existing radio catalogues, but do not have measured redshifts, either because their optical emission is too faint or because of the lack of techniques that can identify candidate high-redshift radio sources (HzRSs). Our study addresses these issues using the Lyman Dropout search technique. This newly built sample probes radio luminosities that are 1–2 orders of magnitude fainter than known radio-active galactic nuclei (AGN) at similar redshifts, thanks to ASKAP’s sensitivity. We investigate the physical origin of radio emission in our sample using a set of diagnostics: (i) radio luminosity at 1.4 GHz, (ii) 1.4 GHz to 3.4 μm flux density ratio, (iii) Far-IR detection, (iv) WISE colour, and (v) SED modelling. The radio/IR analysis has shown that the majority of radio emission in the faint and bright end of our sample’s 887.5 MHz flux density distribution originates from AGN activity. Furthermore, ∼10 per cent of our sample are found to have a 250 μm detection, suggesting a composite system. This suggests that some high-z radio-AGNs are hosted by SB galaxies in contrast to low-z radio-AGNs, which are usually hosted by quiescent elliptical galaxies.

Guzmán-Ortega, Alejandro; Rodriguez-Gomez, Vicente; Snyder, Gregory F; Chamberlain, Katie; Hernquist, Lars

doi: 10.1093/mnras/stac3334pmid: N/A

ABSTRACTUsing the TNG50 cosmological simulation and observations from the Kilo-Degree Survey (KiDS), we investigate the connection between galaxy mergers and optical morphology in the local Universe over a wide range of galaxy stellar masses (8.5 ≤ log (M*/M⊙) ≤ 11).To this end, we have generated over 16 000 synthetic images of TNG50 galaxies designed to match KiDS observations, including the effects of dust attenuation and scattering, and used the statmorph code to measure various image-based morphological diagnostics in the r-band for both data sets. Such measurements include the Gini–M20 and concentration–asymmetry–smoothness statistics. Overall, we find good agreement between the optical morphologies of TNG50 and KiDS galaxies, although the former are slightly more concentrated and asymmetric than their observational counterparts. Afterwards, we trained a random forest classifier to identify merging galaxies in the simulation (including major and minor mergers) using the morphological diagnostics as the model features, along with merger statistics from the merger trees as the ground truth. We find that the asymmetry statistic exhibits the highest feature importance of all the morphological parameters considered. Thus, the performance of our algorithm is comparable to that of the more traditional method of selecting highly asymmetric galaxies. Finally, using our trained model, we estimate the galaxy merger fraction in both our synthetic and observational galaxy samples, finding in both cases that the galaxy merger fraction increases steadily as a function of stellar mass.

Yang, Yingjie; Lu, Xuchen; Qian, Lei; Cao, Shulei

doi: 10.1093/mnras/stac3617pmid: N/A

ABSTRACTTaking advantage of Gaussian process (GP), we obtain an improved estimate of the Hubble constant, H0 = 70.41 ± 1.58 km s−1 Mpc−1, using Hubble parameter [H(z)] from cosmic chronometer (CCH) and expansion rate function [E(z)], extracted from Type Ia supernovae, data. We also use CCH data, including the ones with full covariance matrix, and E(z) data to obtain a determination of $H_0=72.34_{-1.92}^{+1.90}$ km s−1 Mpc−1, which implies that the involvement of full covariance matrix results in higher values and uncertainties of H0. These results are higher than those obtained by directly reconstructing CCH data with GP. In order to estimate the potential of future CCH data, we simulate two sets of H(z) data and use them to constrain H0 by either using GP reconstruction or fitting them with E(z) data. We find that the simulated H(z) data alleviate H0 tension by pushing H0 values higher towards ∼70 km s−1 Mpc−1. We also find that joint H(z) + E(z) data favour higher values of H0, which is also confirmed by constraining H0 in the flat concordance model and second-order Taylor expansion of H(z). In summary, we conclude that more and better-quality CCH data as well as E(z) data can provide a new and useful perspective on resolving H0 tension.

, ; Papadakis, I E; Dovčiak, M; Bursa, M; Karas, V

doi: 10.1093/mnras/stac3625pmid: N/A

ABSTRACTWe study the Fourier time lags due to the Comptonization of disc-emitted photons in a spherical, uniform, and stationary X-ray corona, which located on the rotational axis of the black hole. We use monk, a general relativistic Monte Carlo radiative transfer code, to calculate Compton scattering of photons emitted by a thin disc with a Novikov–Thorne temperature profile. We find that the model time lags due to Comptonization remain constant up to a characteristic frequency and then rapidly decrease to zero at higher frequencies. We provide equations that can be used to determine the time lags and cross-spectra for a wide range of values for the corona radius, temperature, optical depth, height, and for various accretion rates and black hole masses. We also provide an equation for the X-ray luminosity of a single corona, as a function of its characteristics and location above the disc. Remarkably, the observed X-ray time lags of nearby, bright active galaxies can be successfully reproduced by inverse Comptonization process of multiple dynamic coronae.