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1. Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1

   https://doi.org/10.1093/mnras/stac3251  

   Ando, Makoto ; Shimasaku, Kazuhiro ; Ito, Kei ( December 2022 , Monthly Notices of the Royal Astronomical Society)

   Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellarmore »mass limit of $M_{*}=1\times 10^{10}\, {\rm M}_{\odot }$. Finally, we argue that the physical origins of the observed anisotropy should have shorter quenching time-scales than $\sim 1\, \mathrm{Gyr}$, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites must be quenched before their initial orientation angles are significantly changed.

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2. Massive central galaxies of galaxy groups in the Romulus simulations: an overview of galaxy properties at z  = 0

   https://doi.org/10.1093/mnras/stac1622  

   Jung, S. Lyla ; Rennehan, Douglas ; Saeedzadeh, Vida ; Babul, Arif ; Tremmel, Michael ; Quinn, Thomas R. ; Loubser, S. Ilani ; O’Sullivan, E. ; Yi, Sukyoung K. ( June 2022 , Monthly Notices of the Royal Astronomical Society)

   Contrary to many stereotypes about massive galaxies, observed brightest group galaxies (BGGs) are diverse in their star formation rates, kinematic properties, and morphologies. Studying how they evolve into and express such diverse characteristics is an important piece of the galaxy formation puzzle. We use a high-resolution cosmological suite of simulations Romulus and compare simulated central galaxies in group-scale haloes at z = 0 to observed BGGs. The comparison encompasses the stellar mass–halo mass relation, various kinematic properties and scaling relations, morphologies, and the star formation rates. Generally, we find that Romulus reproduces the full spectrum of diversity in the properties of the BGGs very well, albeit with a tendency toward lower than the observed fraction of quenched BGGs. We find both early-type S0 and elliptical galaxies as well as late-type disc galaxies; we find Romulus galaxies that are fast-rotators as well as slow-rotators; and we observe galaxies transforming from late-type to early-type following strong dynamical interactions with satellites. We also carry out case studies of selected Romulus galaxies to explore the link between their properties, and the recent evolution of the stellar system as well as the surrounding intragroup/circumgalactic medium. In general, mergers/strong interactions quench star-forming activity and disrupt themore »stellar disc structure. Sometimes, however, such interactions can also trigger star formation and galaxy rejuvenation. Black hole feedback can also lead to a decline of the star formation rate but by itself, it does not typically lead to complete quenching of the star formation activity in the BGGs.

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3. Galaxy properties as revealed by MaNGA – I. Constraints on IMF and M*/L gradients in ellipticals

   https://doi.org/10.1093/mnras/stz2414  

   Domínguez Sánchez, H ; Bernardi, M ; Brownstein, J R ; Drory, N ; Sheth, R K ( November 2019 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We estimate ages, metallicities, α-element abundance ratios, and stellar initial mass functions (IMFs) of elliptical (E) and S0 galaxies from the MaNGA-DR15 survey. We stack spectra and use a variety of single stellar population synthesis models to interpret the absorption line strengths in these spectra. We quantify how these properties vary across the population, as well as with galactocentric distance. This paper is the first of a series and is based on a sample of pure elliptical galaxies at z ≤ 0.08. We confirm previous work showing that IMFs in Es with the largest luminosity (Lr) and central velocity dispersion (σ0) appear to be increasingly bottom heavy towards their centres. For these galaxies the stellar mass-to-light ratio decreases at most by a factor of 2 from the central regions to Re. In contrast, for lower Lr and σ0 galaxies, the IMF is shallower and M*/Lr in the central regions is similar to the outskirts, although quantitative estimates depend on assumptions about element abundance gradients. Accounting self-consistently for these gradients when estimating both M* and Mdyn brings the two into good agreement: gradients reduce Mdyn by ∼0.2 dex while only slightly increasing the M* inferred using a Kroupa IMF. Thismore »is a different resolution of the M*–Mdyn discrepancy than has been followed in the recent literature where M* of massive galaxies is increased by adopting a Salpeter IMF throughout the galaxy while leaving Mdyn unchanged. A companion paper discusses how stellar population differences are even more pronounced if one separates slow from fast rotators.« less
4. Testing galaxy formation simulations with damped Lyman-α abundance and metallicity evolution

   https://doi.org/10.1093/mnras/staa056  

   Hassan, Sultan ; Finlator, Kristian ; Davé, Romeel ; Churchill, Christopher W. ; Prochaska, J. Xavier ( January 2020 , Monthly Notices of the Royal Astronomical Society)

   We examine the properties of damped Lyman-α absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: simba and technicolor dawn. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multifrequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly α forest mean transmission at z > 5. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at z ≥ 3, and both reproduce the observed neutral hydrogen cosmological mass density, $\Omega _{\rm H\, \small{I}}(z)$. However, the DLA abundance and metallicity distribution are sensitive to the galactic outflows’ feedback and the UVB amplitude. Adopting a strong UVB and/or slow outflows underproduces the observed DLA abundance, but yields broad agreement with the observed DLA metallicity distribution. By contrast, faster outflows eject metals to larger distances, yielding more metal-rich DLAs whose observational selection may be more sensitive to dust bias. The DLA metallicity distribution in models adopting an H2-regulated star formation recipe includes a tail extending to [M/H] ≪ −3, lower than anymore »DLA observed to date, owing to curtailed star formation in low-metallicity galaxies. Our results show that DLA observations play an important role in constraining key physical ingredients in galaxy formation models, complementing traditional ensemble statistics such as the stellar mass and star formation rate functions.

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5. Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters. I. Ages of Quiescent Member Galaxies at 0.3 < z < 1.4

   https://doi.org/10.3847/1538-4357/ac7c0c  

   Khullar, Gourav ; Bayliss, Matthew B. ; Gladders, Michael D. ; Kim, Keunho J. ; Calzadilla, Michael S. ; Strazzullo, Veronica ; Bleem, Lindsey E. ; Mahler, Guillaume ; McDonald, Michael ; Floyd, Benjamin ; et al ( August 2022 , The Astrophysical Journal)

   Abstract Using stellar population synthesis models to infer star formation histories (SFHs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of Sunyaev–Zel’dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < z < 0.9) and three clusters in the SPT Hi-z cluster sample (1.25 < z < 1.4). We analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our data set sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t 50 ) of z = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age–stellar mass relations for the full sample (age of the universemore »at t 50 (Gyr) = 2.52 (±0.04)–1.66 (±0.12) log 10 ( M /10 11 M ⊙ )) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ∼0.75 Gyr earlier than lower-mass galaxies. We also find marginally steeper age–mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass.« less