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ABSTRACT High-redshift ($$z\sim 1$$) galaxy clusters are the domain where environmental quenching mechanisms are expected to emerge as important factors in the evolution of the quiescent galaxy population. Uncovering these initially subtle effects requires exploring multiple dependencies of quenching across the cluster environment, and through time. We analyse the stellar mass functions (SMFs) of 17 galaxy clusters within the GOGREEN and GCLASS surveys in the range $0.8< z<1.5$, and with $$\log {(M/{\rm {M_\odot }})}>9.5$$. The data are fit simultaneously with a Bayesian model that allows the Schechter function parameters of the quiescent and star-forming populations to vary smoothly with cluster-centric radius and redshift. The model also fits the radial galaxy number density profile of each population, allowing the global quenched fraction to be parametrized as a function of redshift and cluster velocity dispersion. We find the star-forming SMF to not depend on radius or redshift. For the quiescent population however, there is $$\sim 2\sigma$$ evidence for a radial dependence. Outside the cluster core ($$R>0.3\, R_{\rm 200}$$), the quenched fraction above $$\log {(M/{\rm {M_\odot }})}=9.5$$ is $$\sim 40{\rm\,\,per\, cent}$$, and the quiescent SMF is similar in shape to the star-forming field. In contrast, the cluster core has an elevated quenched fraction ($$\sim 70{\rm \,\,per\, cent}$$), and a quiescent SMF similar in shape to the quiescent field population. We explore contributions of ‘early mass-quenching’ and mass-independent ‘environmental-quenching’ models in each of these radial regimes. The core is well described primarily by early mass-quenching, which we interpret as accelerated quenching of massive galaxies in protoclusters, possibly through merger-driven feedback mechanisms. The non-core is better described through mass-independent environmental-quenching of the infalling field population. 

ABSTRACT Understanding the processes that transform star-forming galaxies into quiescent ones is key to unravelling the role of environment in galaxy evolution. We present measurements of the luminosity functions (LFs) and stellar mass functions (SMFs) of passive red-sequence galaxies in four galaxy clusters at $0.8 < z < 1.3$, selected using deep Very Large Telescope (VLT) observations complemented with data from the Gemini CLuster Astrophysics Spectroscopic (GCLASS) and Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) surveys. We find a significant enhancement in the abundance of faint/low-mass passive galaxies in both the LFs and SMFs of all four clusters compared to the field. This is further evidenced by a shallower low-mass slope in the composite passive cluster SMF, which yields a Schechter parameter $$\alpha = -0.54^{+\, 0.03}_{-0.03}$$, compared to $$\alpha = 0.12^{+\, 0.01}_{-0.01}$$ for the field. Our findings indicate that quenching processes that act in clusters are enhanced compared to the field, suggesting that environmental quenching mechanisms may already be active by $$z\sim 1$$. To reproduce the observed passive cluster SMF, we estimate that $$25\pm 5~{{\ \rm per\ cent}}$$ of the star-forming field population that falls into the cluster must have been quenched. Our results largely support traditional quenching models but highlight the need for deeper studies of larger cluster samples to better understand the role of environmental quenching in the distant Universe. 

Abstract The changes in colors across a galaxy are intimately connected to the galaxy’s formation, growth, quenching history, and dust content. A particularly important epoch in the growth of galaxies is nearz∼ 2, often referred to as “cosmic noon,” where galaxies on average reach the peak of their star formation. We study a population of 125 cluster galaxies atz∼ 1.6 in three Hubble Space Telescope filters, F475W, F625W, and F160W, roughly corresponding to the rest-frame far-ultraviolet, near-ultraviolet, andrband, respectively. By comparing to a control sample of 200 field galaxies at similar redshift, we reveal clear, statistically significant differences in the overall spatially resolved colors and color gradients in galaxies across these two different environments. On average, cluster galaxies have redder ultraviolet colors in both the inner and outer regions bounded byr₅₀, as well as an overall wider dispersion of outside-in color gradients. The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content. 

Abstract We examine the quiescent fractions of massive galaxies in sixz≳ 3 spectroscopically confirmed protoclusters in the COSMOS field, one of which is newly confirmed and presented here. We report the spectroscopic confirmation of MAGAZ3NE J100143+023021 at $z={3.122}_{-0.004}^{+0.007}$by the Massive Ancient Galaxies Atz> 3 NEar-infrared (MAGAZ3NE) survey. MAGAZ3NE J100143+023021 contains a total of 79 protocluster members (28 spectroscopic and 51 photometric). Three spectroscopically confirmed members are star-forming ultramassive galaxies (UMGs; $\log (M_{\star }/M_{\odot })$> 11), the most massive of which has $\log (M_{\star }/M_{\odot })$ $={11.15}_{-0.06}^{+0.05}$. Combining Keck/MOSFIRE spectroscopy and the COSMOS2020 photometric catalog, we use a weighted Gaussian kernel density estimator to map the protocluster and measure its total mass ${2.25}_{-0.65}^{+1.55}\times {10}^{14}{M}_{\odot }$in the dense “core” region. For each of the six COSMOS protoclusters, we compare the quiescent fraction to the status of the central UMG as star-forming or quiescent. We observe that galaxies in these protoclusters appear to obey galactic conformity: Elevated quiescent fractions are found in protoclusters withUVJ-quiescent UMGs and low quiescent fractions are found in protoclusters containingUVJstar-frming UMGs. This correlation of star formation/quiescence in UMGs and the massive galaxies nearby in these protoclusters is the first evidence for the existence of galactic conformity atz> 3. Despite disagreements over mechanisms behind conformity at low redshifts, its presence at these early cosmic times would provide strong constraints on the physics proposed to drive galactic conformity. 

Abstract We present rest-frame optical spectra from Keck/MOSFIRE and Keck/NIRES of 16 candidate ultramassive galaxies targeted as part of the Massive Ancient Galaxies atz> 3 Near-Infrared Survey (MAGAZ3NE). These candidates were selected to have photometric redshifts 3 ≲z_phot<4, photometric stellar masses $\log \left(M_{\ast }/M_{\odot }\right)$> 11.7, and well-sampled photometric spectral energy distributions (SEDs) from the UltraVISTA and VIDEO surveys. In contrast to previous spectroscopic observations of blue star-forming and poststarburst ultramassive galaxies, candidates in this sample have very red SEDs implying significant dust attenuation, old stellar ages, and/or active galactic nuclei (AGN). Of these galaxies, eight are revealed to be heavily dust-obscured 2.0 <z< 2.7 galaxies with strong emission lines, some showing broad features indicative of AGN, three are Type I AGN hosts atz> 3, one is az∼ 1.2 dusty galaxy, and four galaxies do not have a confirmed spectroscopic redshift. In fact, none of the sample has ∣z_spec−z_phot∣ < 0.5, suggesting difficulties for photometric redshift programs in fitting similarly red SEDs. The prevalence of these red interloper galaxies suggests that the number densities of high-mass galaxies are overestimated atz≳ 3 in large photometric surveys, helping to resolve the “impossibly early galaxy problem” and leading to much better agreement with cosmological galaxy simulations. A more complete spectroscopic survey of ultramassive galaxies is required to pin down the uncertainties on their number densities in the early Universe. 

Abstract We present an analysis of the number density of galaxies as a function of stellar mass (i.e., the stellar mass function (SMF)) in the COSMOS field atz∼ 3.3, making a comparison between the SMF in overdense environments and the SMF in the coeval field. In particular, this region contains the Elentári proto-supercluster, a system of six extended overdensities spanning ∼70 cMpc on a side. A clear difference is seen in the high-mass slope of these SMFs, with overdense regions showing an increase in the ratio of high-mass galaxies to low-mass galaxies relative to the field, indicating a more rapid buildup of stellar mass in overdense environments. This result qualitatively agrees with analyses of clusters atz∼ 1, though the differences between protocluster and field SMFs atz∼ 3.3 are smaller. While this is consistent with overdensities enhancing the evolution of their member galaxies, potentially through increased merger rates, whether this enhancement begins in protocluster environments or even earlier in group environments is still unclear. Though the measured fractions of quiescent galaxies between the field and overdense environments do not vary significantly, implying that this stellar mass enhancement is ongoing and any starbursts triggered by merger activity have not yet quenched, we note that spectroscopic observations are biased toward star-forming populations, particularly for low-mass galaxies. If mergers are indeed responsible, high-resolution imaging of Elentári and similar structures at these early epochs should then reveal increased merger rates relative to the field. Larger samples of well-characterized overdensities are necessary to draw broader conclusions in these areas. 

ABSTRACT We explore models of massive (>1010 M⊙) satellite quenching in massive clusters at z ≳ 1 using an MCMC framework, focusing on two primary parameters: Rquench (the host-centric radius at which quenching begins) and τquench (the time-scale upon which a satellite quenches after crossing Rquench). Our MCMC analysis shows two local maxima in the 1D posterior probability distribution of Rquench at approximately 0.25 and 1.0 R200. Analysing four distinct solutions in the τquench–Rquench parameter space, nearly all of which yield quiescent fractions consistent with observational data from the GOGREEN survey, we investigate whether these solutions represent distinct quenching pathways and find that they can be separated between ‘starvation’ and ‘core quenching’ scenarios. The starvation pathway is characterized by quenching time-scales that are roughly consistent with the total cold gas (H2 + H i) depletion time-scale at intermediate z, while core quenching is characterized by satellites with relatively high line-of-sight velocities that quench on short time-scales (∼0.25 Gyr) after reaching the inner region of the cluster (<0.30 R200). Lastly, we break the degeneracy between these solutions by comparing the observed properties of transition galaxies from the GOGREEN survey. We conclude that only the ‘starvation’ pathway is consistent with the projected phase-space distribution and relative abundance of transition galaxies at z ∼ 1. However, we acknowledge that ram pressure might contribute as a secondary quenching mechanism. 

Abstract The Local Volume Complete Cluster Survey is an ongoing program to observe nearly a hundred low-redshift X-ray-luminous galaxy clusters (redshifts 0.03 <z< 0.12 and X-ray luminosities in the 0.1–2.4 keV bandL_X500c> 10⁴⁴erg s⁻¹) with the Dark Energy Camera, capturing data in theu,g,r,i,zbands with a 5σpoint source depth of approximately 25th–26th AB magnitudes. Here, we map the aperture masses in 58 galaxy cluster fields using weak gravitational lensing. These clusters span a variety of dynamical states, from nearly relaxed to merging systems, and approximately half of them have not been subject to detailed weak lensing analysis before. In each cluster field, we analyze the alignment between the 2D mass distribution described by the aperture mass map, the 2D red-sequence (RS) galaxy distribution, and the brightest cluster galaxy (BCG). We find that the orientations of the BCG and the RS distribution are strongly aligned throughout the interiors of the clusters: the median misalignment angle is 19° within 2 Mpc. We also observe the alignment between the orientations of the RS distribution and the overall cluster mass distribution (by a median difference of 32° within 1 Mpc), although this is constrained by galaxy shape noise and the limitations of our cluster sample size. These types of alignment suggest long-term dynamical evolution within the clusters over cosmic timescales. 

ABSTRACT Motivated by spectroscopic confirmation of three overdense regions in the COSMOS field at z ∼ 3.35, we analyse the uniquely deep multiwavelength photometry and extensive spectroscopy available in the field to identify any further related structure. We construct a three-dimensional density map using the Voronoi tesselation Monte Carlo method and find additional regions of significant overdensity. Here, we present and examine a set of six overdense structures at 3.20 < z < 3.45 in the COSMOS field, the most well-characterized of which, PCl J0959 + 0235, has 80 spectroscopically confirmed members and an estimated mass of 1.35 × 1015 M⊙, and is modelled to virialize at z ∼ 1.5−2.0. These structures contain 10 overdense peaks with >5σ overdensity separated by up to 70 cMpc, suggestive of a proto-supercluster similar to the Hyperion system at z ∼ 2.45. Upcoming photometric surveys with JWST such as COSMOS-Web, and further spectroscopic follow-up will enable more extensive analysis of the evolutionary effects that such an environment may have on its component galaxies at these early times. 

Abstract We present the first results from the Web Epoch of Reionization LyαSurvey (WERLS), a spectroscopic survey of Lyαemission using Keck I/MOSFIRE and LRIS. WERLS targets bright (J< 26) galaxy candidates with photometric redshifts of 5.5 ≲z≲ 8 selected from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11z∼ 7–8 Lyαemitters (LAEs; three secure and eight tentative candidates) detected in the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield is ∼13%, which is broadly consistent with expectations assuming some loss from redshift uncertainty, contamination from sky OH lines, and that the Universe is approximately half-ionized at this epoch, whereby observable Lyαemission is unlikely for galaxies embedded in a neutral intergalactic medium. Our targets are selected to be UV-bright, and span a range of absolute UV magnitudes with −23.1 <M_UV< −19.8. With two LAEs detected atz= 7.68, we also consider the possibility of an ionized bubble at this redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for pinpointing beacons of reionization and mapping the large-scale distribution of mass relative to the ionization state of the Universe.