Search

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]

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]

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 SMF of 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). [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]

Central galaxies (CGs) in massive halos live in unique environments with formation histories closely linked to that of the host halo. In local clusters, they have larger sizes (Re) and lower velocity dispersions (σ) at fixed stellar mass M*, and much larger Re at a fixed σ than field and satellite galaxies (non-CGs). Using spectroscopic observations of group galaxies selected from the COSMOS survey, we compare the dynamical scaling relations of early-type CGs and non-CGs at z ∼ 0.6 to distinguish possible mechanisms that produce the required evolution. CGs are systematically offset toward larger Re at fixed σ compared to non-CGs with similar M*. The CG Re-M* relation also shows differences, primarily driven by a subpopulation (∼15%) of galaxies with large Re, while the M*-σ relations are indistinguishable. These results are accentuated when double Sérsic profiles, which better fit light in the outer regions of galaxies, are adopted. They suggest that even group-scale CGs can develop extended components by these redshifts that can increase total Re and M* estimates by factors of ∼2. To probe the evolutionary link between our sample and cluster CGs, we also analyze two cluster samples at z ∼ 0.6 and z ∼ 0. We find similar results for the more massive halos at comparable z, but much more distinct CG scaling relations at low-z. Thus, the rapid, late-time accretion of outer components, perhaps via the stripping and accretion of satellites, would appear to be a key feature that distinguishes the evolutionary history of CGs. [ABSTRACT FROM AUTHOR]

Locating the centers of dark matter halos is critical for understanding the mass profiles of halos, as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper, we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray-selected galaxy groups in the COSMOS field with redshifts 0 < z < 1 and halo masses in the range 1013-1014M☼. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to ≲ 75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically ∼50-150 kpc). Approximately 30% of groups in our sample have ambiguous centers with multiple bright or massive galaxies, and some of these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5%-30% if inaccurate centers are used and the issue of miscentering is not addressed. [ABSTRACT FROM AUTHOR]