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We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109M⊙. Taking advantage of > 4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct threedimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of starforming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMFof field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at zstart = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to zfinal = 0.8 following empirical prescriptions for star-formation, quenching and galaxy-galaxy merging.We run the simulationmultiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).

The origin of the quenching in galaxies is still highly debated. Different scenarios and processes are proposed. We use multiband (400–1600 nm) bulge–disc decompositions of massive galaxies in the redshift range 0 < z < 2 to explore the distribution and the evolution of galaxies in the |$\log \, {\rm SFR-log}\: M_{*}$| plane as a function of the stellar mass weighted bulge-to-total ratio (⁠|$B/T_{M_{*}}$|⁠) and also for internal galaxy components (bulge/disc) separately. We find evidence of a clear link between the presence of a bulge and the flattening of the main sequence in the high-mass end. All bulgeless galaxies (⁠|$B/T_{M_{*}}$| < 0.2) lie on the main sequence, and there is little evidence of a quenching channel without bulge growth. Galaxies with a significant bulge component (⁠|$B/T_{M_{*}}$| > 0.2) are equally distributed in number between star forming and passive regions. The vast majority of bulges in the main-sequence galaxies are quiescent, while star formation is localized in the disc component. Our current findings underline a strong correlation between the presence of the bulge and the star formation state of the galaxy. A bulge, if present, is often quiescent, independently of the morphology or the star formation activity of the host galaxy. Additionally, if a galaxy is quiescent, with a large probability, is hosting a bulge. Conversely, if the galaxy has a discy shape is highly probable to be star forming. [ABSTRACT FROM AUTHOR]

We present a search for disturbed, candidate ram pressure stripping galaxies across more than 50 spectroscopically selected SDSS groups and clusters. 48 ram pressure candidates are visually identified in these systems using high-quality UNIONS imaging from the Canada-France-Hawaii Telescope, covering |${\sim }6200\, \mathrm{deg^2}$| and |${\sim }2800\, \mathrm{deg^2}$| in the u - and r -bands, respectively. Ram pressure candidates are found in groups and clusters spanning a wide range in halo mass and include ∼30 ram pressure candidates in the group regime (Mh < 1014). The observed frequency of ram pressure candidates shows substantial scatter with group/cluster mass, but on average is larger in clusters (⁠|$M_h \ge 10^{14}\, \mathrm{M_\odot }$|⁠) than groups (⁠|$M_h \lt 10^{14}\, \mathrm{M_\odot }$|⁠) by a factor of ∼2. We find that ram pressure candidates are most commonly low-mass galaxies and have enhanced star formation rates relative to star-forming field galaxies. The enhancement in star formation is largely independent of galaxy mass and strongest for galaxies in clusters. As a result of the large survey footprint and excellent image quality from UNIONS, we are able to identify disturbed galaxies, potentially affected by ram pressure stripping, across a wide range of host environment. [ABSTRACT FROM AUTHOR]

Passive early-type galaxies dominate cluster cores at z ≲ 1.5. At higher redshift, cluster core galaxies are observed to have on-going star-formation, which is fueled by cold molecular gas. We measured the molecular gas reservoir of the central region around the radio-loud active galactic nucleus (AGN) in the cluster CARLA J1103 + 3449 at z = 1.44 using NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measured its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71–94.5 GHz, and assuming Ssynch ∝ ν−α, we obtain a flat spectral index of α = 0.14 ± 0.03 for the AGN core emission, and a steeper index of α = 1.43 ± 0.04 and α = 1.15 ± 0.04 at positions close to the western and eastern lobes, respectively. The total spectral index is α = 0.92 ± 0.02 over the range 73.8 MHz–94.5 GHz. We detect two CO(2–1) emission lines, both blueshifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc southeast and ~14 kpc southwest of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of Mgastot = 3.9 ± 0.4 × 1010M⊙ $M^{\rm{tot}}_{\rm{gas}} = 3.9 \pm 0.4 \times 10^{10}\,M_{\odot}$ M gas tot = 3.9 ± 0.4 × 10 10   M ⊙ , which dominates (≳60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (star formation rate ~30–140 M⊙ yr−1), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star formation before quiescence. The other confirmed cluster members show star formation rates at ~2σ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field. [ABSTRACT FROM AUTHOR]

We study the evidence for a diversity of formation processes in early-type galaxies by presenting the first complete volume-limited sample of slow rotators with both integral-field kinematics from the ATLAS3D Project and high spatial resolution photometry from the Hubble Space Telescope. Analysing the nuclear surface brightness profiles of 12 newly imaged slow rotators, we classify their light profiles as core-less, and place an upper limit to the core size of about 10 pc. Considering the full magnitude and volume-limited ATLAS3D sample, we correlate the presence or lack of cores with stellar kinematics, including the proxy for the stellar angular momentum (λRe) and the velocity dispersion within one half-light radius (σe), stellar mass, stellar age, α-element abundance, and age and metallicity gradients. More than half of the slow rotators have core-less light profiles, and they are all less massive than 1011 M. Core-less slow rotators show evidence for counter-rotating flattened structures, have steeper metallicity gradients, and a larger dispersion of gradient values (Δ[Z/H] = -0.42 ± 0.18) than core slow rotators (Δ[Z/H] = -0.23 ± 0.07). Our results suggest that core and core-less slow rotators have different assembly processes, where the former, as previously discussed, are the relics of massive dissipation-less merging in the presence of central supermassive black holes. Formation processes of core-less slow rotators are consistent with accretion of counter-rotating gas or gas-rich mergers of special orbital configurations, which lower the final net angular momentum of stars, but support star formation. We also highlight core fast rotators as galaxies that share properties of core slow rotators (i.e. cores, ages, σe, and population gradients) and core-less slow rotators (i.e. kinematics, Re, mass, and larger spread in population gradients). Formation processes similar to those for core-less slow rotators can be invoked to explain the assembly of core fast rotators, with the distinction that these processes form or preserve cores. [ABSTRACT FROM AUTHOR]

We study the rest-frame optical mass–size relation of bulges and discs from z ∼ 2 to z ∼ 0 for a complete sample of massive galaxies in the CANDELS fields using two-component Sérsic models. Discs and star-forming galaxies follow similar mass–size relations. The mass–size relation of bulges is less steep than the one of quiescent galaxies (best-fitting slope of 0.7 for quiescent galaxies against 0.4 for bulges). We find little dependence of the structural properties of massive bulges and discs with the global morphology of galaxies (disc versus bulge dominated) and the star formation activity (star-forming versus quiescent). This result suggests similar bulge formation mechanisms for most massive galaxies and also that the formation of the bulge component does not significantly affect the disc structure. Our results pose a challenge to current cosmological models that predict distinct structural properties for stellar bulges arising from mergers and disc instabilities. [ABSTRACT FROM AUTHOR]

We present a study of the star formation rate (SFR)–density relation at |$z$| ∼ 0.9 using data drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We find that SFR does depend on environment, but only for intermediate-stellar mass galaxies (1010.1 < M */M⊙ < 1010.8) wherein the median SFR at the highest densities is 0.2–0.3 dex less than at lower densities at a significance of 4σ. Galaxies that are more/less massive than this have SFRs that vary at most by |${\approx }20{{\ \rm per\ cent}}$| across all environments, but show no statistically significant trend. We further split galaxies into low-redshift (⁠|$z$| ∼ 0.8) and high-redshift (⁠|$z$| ∼ 1.05) subsamples and observe nearly identical behaviour. We devise a simple toy model to explore possible star formation histories for galaxies evolving between these redshifts. The key assumption in this model is that star-forming galaxies in a given environment-stellar mass bin can be described as a superposition of two exponential time-scales (SFR ∝  e − t /τ): a long−τ time-scale with τ = 4 Gyr to simulate 'normal' star-forming galaxies, and a short-τ time-scale with free τ (between 0.3 ≤ τ/Gyr ≤ 2) to simulate galaxies on a quenching trajectory. In general, we find that galaxies residing in low/high environmental densities are more heavily weighted to the long-τ/short-τ pathways, respectively, which we argue is a signature of environmental quenching. Furthermore, for intermediate-stellar mass galaxies this transition begins at intermediate-density environments suggesting that environmental quenching is relevant in group-like haloes and/or cluster infall regions. [ABSTRACT FROM AUTHOR]

High-redshift galaxy clusters allow us to examine galaxy formation in extreme environments. Here we compile data for 15 z > 1 galaxy clusters to test the predictions from a state-ofthe- art semi-analytical model of galaxy formation. The model gives a good match to the slope and zero-point of the cluster red sequence. The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but underestimates the number of galaxies around the break in the cluster luminosity function. We find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy luminosity function, but worsens the predictions for the red sequence at bright magnitudes. Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is large due to these galaxies having large reservoirs of cold gas as well as small radii. We find that matching the luminosity function and colours of high-redshift cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models. [ABSTRACT FROM AUTHOR]

We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (ϵ > 0.2) and intermediate to high luminosities (Mz < -19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, wealso find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and that the present-day major axis is an indicator of the preferred merging axis. [ABSTRACT FROM AUTHOR]

The final stages of mass assembly of present-day massive galaxies are expected to occur through the accretion of multiple satellites. Cosmological simulations thus predict a high frequency of stellar streams resulting from this mass accretion around the massive galaxies in the Local Volume. Such tidal streams are difficult to observe, especially in dense cluster environments, where they are readily destroyed. We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird telescope. Using the deeper, higher-resolution, and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already cataloged Virgo Cluster Catalog dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g -- i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of the so-called pre-processing before it gets affected by the cluster environment, or in a group which already ventured toward the central regions of Virgo Cluster. In any case, compared to the other spiral galaxies in the Virgo Cluster, but also to those located in lower density environments, NGC 4216 seems to suffer an unusually heavy bombardment. Further studies will be needed to determine whether, given the surface brightness limit of our survey, about 29 mag arcsec-2, the number of observed streams around that galaxy is as predicted by cosmological simulations or conversely, whether the possible lack of similar structures in other galaxies poses a challenge to the merger-based model of galaxy mass assembly. [ABSTRACT FROM AUTHOR]

Unveiling the structural evolution of spheroids, and in particular the origin of the tight size- stellar mass relation, has become one of the hottest topics in cosmology in the last years and it is still largely debated. To this purpose, we present and discuss basic predictions of an updated version of the latest release of the Munich semi-analytic hierarchical galaxy formation model that grows bulges via mergers and disc instabilities. We find that while spheroids below a characteristic mass Ms ~ 1011M⊙ grow their sizes via a mixture of disc instability and mergers, galaxies above it mainly evolve via dry mergers. Including gas dissipation in major mergers efficiently shrinks galaxies, especially those with final mass Ms ≲ 1011M⊙ that are the most gas-rich, improving the match with different observables. We find that the predicted scatter in sizes at fixed stellar mass is still larger than the observed one by up to≲40 per cent. Spheroids are, on average, more compact at higher redshifts at fixed stellar mass, and at fixed redshift and stellar mass larger galaxies tend to be more star forming. More specifically, while for bulge-dominated galaxies the model envisages a nearly mass-independent decrease in sizes, the predicted size evolution for intermediate-mass galaxies is more complex. The z = 2 progenitors of massive galaxies with Mstar ~ (1-2) × 1011M⊙ and B/T > 0.7 at z = 0 are found to be mostly disc-dominated galaxies with a median B/T ~ 0.3, with only ~20 per cent remaining bulge-dominated. The model also predicts that central spheroids living in more massive haloes tend to have larger sizes at fixed stellar mass. Including host halo mass dependence in computing velocity dispersions allows the model to properly reproduce the correlations with stellar mass. We also discuss the Fundamental Plane, the correlations with galaxy age, the structural properties of pseudo-bulges and the correlations with central black holes. [ABSTRACT FROM AUTHOR]