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Radio Active Galactic Nuclei (RAGNs) are mainly found in dense structures (i.e., clusters/groups) at redshifts of z$<$2 and are commonly used to detect protoclusters at higher redshift. Here, we attempt to study the host and environmental properties of two relatively faint ($\mathrm L_\mathrm{1.4GHz} \sim10^{25}$ W Hz$^{-1}$) RAGNs in a known protocluster at z=3.3 in the PCl J0227-0421 field, detected using the latest radio observation obtained as part of the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) Survey. Using new spectroscopic observations obtained from Keck/MOSFIRE as part of the Charting Cluster Construction with the VIMOS Ultra-Deep Survey (VUDS) and ORELSE (C3VO) survey and previous spectroscopic data obtained as part of the VIMOS-VLT Deep Survey (VVDS) and VUDS, we revise the three-dimensional overdensity field around this protocluster. The protocluster is embedded in a large scale overdensity protostructure. This protostructure has an estimated total mass of $\sim$2.6$\times10^{15} M_\odot$ and contains several overdensity peaks. Both RAGNs are hosted by very bright and massive galaxies, while their hosts show extreme differences color, indicating that they have different ages and are in different evolutionary stages. Furthermore, we find that they are not in the most locally dense parts of the protostructure, but are fairly close to the centers of their parent overdensity peaks. We propose a scenario where merging might already have happened in both cases, which lowered the local density of their surrounding area and boosted their stellar mass. This work is the first time that two RAGNs at low luminosity have been found and studied within a high redshift protostructure., Comment: 23 pages, 11 figures, 4 tables, accepted by ApJ

The shape of bent, double-lobed radio sources requires a dense gaseous medium. Bent sources can therefore be used to identify galaxy clusters and characterize their evolutionary history. By combining radio observations from the Very Large Array Faint Images of the Radio Sky at Twenty centimeters (VLA FIRST) survey with optical and infrared imaging of 36 red sequence selected cluster candidates from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 < z < 2.2), we find that radio sources with narrower opening angles reside in richer clusters, indicating that the cluster environment impacts radio morphology. Within these clusters, we determine 55.5% of our radio host galaxies are brightest cluster galaxies (BCGs) and that the remainder are associated with other luminous galaxies. The projected separations between the radio sources and cluster centers and the sizes of the opening angles of bent sources follow similar distributions for BCG and non-BCG host populations, suggesting that COBRA host galaxies are either BCGs or galaxies that may evolve into BCGs. By measuring the orientation of the radio sources relative to the cluster centers, we find between 30% and 42% of COBRA bent sources are outgoing and have passed through the cluster center, while between 8% and 58% of COBRA bent sources are infalling. Although these sources typically do not follow directly radial paths, the large population of outgoing sources contrasts what is observed in low-z samples of bent sources and may indicate that the intracluster medium is less dense in these high-z clusters., Comment: 29 pages, 18 figures, 2 tables. Accepted to ApJ on November 23, 2020

Recent hydrodynamic simulations and observations of radio jets have shown that the surrounding environment has a large effect on their resulting morphology. To investigate this we use a sample of 50 Extended Radio Active Galactic Nuclei (ERAGN) detected in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. These sources are all successfully cross-identified to galaxies within a redshift range of $0.55 \leq z \leq 1.35$, either through spectroscopic redshifts or accurate photometric redshifts. We find that ERAGN are more compact in high-density environments than those in low-density environments at a significance level of 4.5$\sigma$. Among a series of internal properties under our scrutiny, only the radio power demonstrates a positive correlation with their spatial extent. After removing the possible radio power effect, the difference of size in low- and high-density environments persists. In the global environment analyses, the majority (86\%) of high-density ERAGN reside in the cluster/group environment. In addition, ERAGN in the cluster/group central regions are preferentially compact with a small scatter in size, compared to those in the cluster/group intermediate regions and fields. In conclusion, our data appear to support the interpretation that the dense intracluster gas in the central regions of galaxy clusters plays a major role in confining the spatial extent of radio jets.

Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at $z=0.923$ using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrow-band filter, NB1261, matches to H$\alpha$ emission from the cluster at $z=0.923$. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H$\alpha$ emitters associated with the cluster. They have significant overlap with MIPS 24$\mu$m sources and are located exclusively in the star forming regime on the rest-frame $UVJ$ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment; cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase., Comment: 19 pages, 15 figures. Accepted for publication in ApJ. Error bars in Table 2 corrected

To understand how strong emission line galaxies (ELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target Strong ELGs (SELGs) from the ZFOURGE imaging survey that have blended (Hb+[OIII]) rest-frame equivalent widths of >230A and 2.560%, i.e. the inferred gas masses can easily fuel a starburst to double stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that 1) strong [OIII]5007A emission signals an early episode of intense stellar growth in low mass (Mstar<0.1M*) galaxies and 2) many, if not most, galaxies at z>3 go through this starburst phase. If true, low-mass galaxies with strong [OIII]5007A emission (EW_rest>200A) may be an increasingly important source of ionizing UV radiation at z>3., Comment: Astrophysical Journal, in press

In this study we investigate 179 radio-IR galaxies drawn from a sample of spectroscopically-confirmed galaxies that are detected in radio and mid-infrared (MIR) in the redshift range of $0.55 \leq z \leq 1.30$ in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We constrain the Active Galactic Nuclei (AGN) contribution in the total IR luminosity (f$_{\text{AGN}}$), and estimate the AGN luminosity (L$_{\text{AGN}}$) and the star formation rate (SFR) using the CIGALE Spectral Energy Distribution (SED) fitting routine. Based on the f$_{\text{AGN}}$ and radio luminosity, radio-IR galaxies are split into: galaxies that host either high or low f$_{\text{AGN}}$ AGN (high-/low-f$_{\text{AGN}}$), and star forming galaxies with little to no AGN activity (SFGs). We study the colour, stellar mass, radio luminosity, L$_{\text{AGN}}$ and SFR properties of the three radio-IR sub-samples, comparing to a spec-IR sample drawn from spectroscopically-confirmed galaxies that are also detected in MIR. No significant difference between radio luminosity of these sub-samples was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between L$_{\text{AGN}}$and specific SFR (sSFR) for both AGN sub-samples, strongly suggesting a co-evolution scenario of AGN and SF in these galaxies. A toy model is designed to demonstrate this co-evolution scenario, where we find that, in almost all cases, a rapid quenching timescale is required, which we argue is a signature of AGN quenching. The environmental preference for intermediate/infall regions of clusters/groups remains across the co-evolution scenario, which suggests that galaxies might be in an orbital motion around the cluster/group during the scenario.

We measure the fraction of galaxy-galaxy mergers in two clusters at $z\sim2$ using imaging and grism observations from the {\it Hubble Space Telescope}. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the {\it Spitzer Space Telescope}, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the $z\sim1.6$ cluster (IRC0222A) and G141 for the $z\sim2$ cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of $11_{-3.2}^{+8.2}$ in IRC0222A and $18_{-4.5}^{+7.8}$ in IRC0222B. In comparison, we measure a merger fraction of $5.0_{-0.8}^{+1.1}\%$ for field galaxies at $z\sim2$. Our study indicates that the galaxy-galaxy merger fraction in clusters at $z\sim2$ is enhanced compared the field population, but note that more cluster measurements at this epoch are needed to confirm our findings.

Using 57 Radio Active Galactic nuclei (RAGN) at 0.55 $\leq$ z $\leq$ 1.3 drawn from five fields of the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, we study the effect of injection of energy from outbursts of RAGN on their spectroscopically-confirmed neighboring galaxies (SNGs). We observe an elevated fraction of quenched neighbors (fq) within 500 kpc projected radius of RAGN in the most dense local environments compared to those of non-RAGN control samples matched to the RAGN population in colour, stellar mass, and local environment at 2$\sigma$ significance. Further analyses show that there are offsets at similar significance between fqs of RAGN-SNGs and the appropriate control samples for galaxies specifically in cluster environments and those hosted by most massive cluster galaxies, which tentatively suggests that some negative feedback from the RAGN is occurring in these dense environments. In addition, we find that the median radio power of RAGN increases with increasing local overdensity, an effect which may lend itself to the quenching of neighboring galaxies. Furthermore, we find that, in the highest local overdensities, the fq of the sub-sample of lower stellar mass RAGN-SNGs is larger than that of the higher stellar mass RAGN-SNGs sub-sample, which indicates a more pronounced effect from RAGN on lower stellar mass galaxies. We propose a scenario in which RAGN residing within clusters might heat the intracluster medium (ICM) affecting both in situ star formation and any inflowing gas that remains in their neighboring galaxies., Comment: submitted to MNRAS, 15 pages, 2 tables and 6 figures, comments welcome

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 (10^10.1 < M* / Msol < 10^10.8) wherein the median SFR at the highest densities is 0.2-0.3 dex less than at lower densities at a significance of 4 sigma. Interestingly, mass does not drive SFR; galaxies that are more/less massive have SFRs that vary at most by ~20% across all environments showing no statistically significant dependence. We further split galaxies into low-redshift (z ~ 0.8) and high-redshift (z ~ 1.05) subsamples and observe nearly identical behavior. We devise a simple toy model to explore possible star-formation histories (SFHs) 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 timescales (SFR ~ e^(-t/tau)): a long-tau timescale with tau = 4 Gyr to simulate "normal" star-forming galaxies, and a short-tau timescale with free tau (between 0.3 < tau/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-tau/short-tau 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 halos and/or cluster infall regions., Comment: 17 pages, 7 figures

Using ~5000 spectroscopically-confirmed galaxies drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey we investigate the relationship between color and galaxy density for galaxy populations of various stellar masses in the redshift range $0.55 \le z \le 1.4$. The fraction of galaxies with colors consistent with no ongoing star formation ($f_q$) is broadly observed to increase with increasing stellar mass, increasing galaxy density, and decreasing redshift, with clear differences observed in $f_q$ between field and group/cluster galaxies at the highest redshifts studied. We use a semi-empirical model to generate mock group/cluster galaxies unaffected by environmental processes and compare them to observed populations to constrain the environmental quenching efficiency ($\Psi_{convert}$). High-density environments from $0.55 \le z \le 1.4$ appear capable of efficiently quenching galaxies with $\log(M_{\ast}/M_{\odot})>10.45$. Lower stellar mass galaxies also appear efficiently quenched at the lowest redshifts, but this efficiency drops precipitously with increasing redshift. Quenching efficiencies, combined with simulated group/cluster accretion histories and results from a companion ORELSE study, are used to constrain the average time from group/cluster accretion to quiescence and the time between accretion and the inception of quenching. These timescales were constrained to be <$t_{convert}$>=$2.4\pm0.3$ and <$t_{delay}$>=$1.3\pm0.4$ Gyr, respectively, for galaxies with $\log(M_{\ast}/M_{\odot})>10.45$ and <$t_{convert}$>=$3.3\pm0.3$ and <$t_{delay}$>=$2.2\pm0.4$ Gyr for lower stellar mass galaxies. These quenching efficiencies and associated timescales are used to rule out certain environmental mechanisms as being those primarily responsible for transforming the star-formation properties of galaxies over this 4 Gyr window in cosmic time., Comment: 26 pages, 8 Figures, 4 Tables. Updated with the accepted MNRAS version that includes minor changes to the analysis and text

We present an investigation of the dependence of galaxy kinematics on the environment for a sample of 94 star-forming galaxies at $z\sim0.9$ from the ORELSE survey. ORELSE is a large photometric and spectroscopic campaign dedicated to mapping out and characterizing galaxy properties across a full range of environments in 15 fields containing large-scale structures (LSSs) in a redshift range of $0.6 < z < 1.3$. We constrained the rotation velocity for our kinematic sample in an ORELSE field, containing the SC1604 supercluster, by fitting high-resolution semi-analytical models to the data. We constructed the stellar-mass/B-band Tully-Fisher relation and found no dependence of the intrinsic scatter on both local and global environment. Moreover, we compared the stellar-to-dynamical mass ratio ($M_\ast/M_{dyn}$) of SC1604 galaxies to those residing in less dense local environment by leveraging data from the HR-COSMOS sample. We found that, at fixed stellar mass, SC1604 galaxies have $\sim30\%$ smaller dynamical masses on average. By comparing the distributions of the galaxy parameters that define $M_{dyn}$ (i.e., circular velocity and the characteristic radius $r_{2.2}$) between SC1604 and HR-COSMOS, we found that smaller dynamical masses are mostly caused by smaller $r_{2.2}$ for SC1604 galaxies. We also observed that SC1604 galaxies in general show $\sim20\%$ lower stellar specific angular momentum ($j_\ast$) with respect to the HR-COSMOS sample. Adopting literature estimates for (1) the excess rate of galaxy-galaxy mergers in intermediate/high-density environments and (2) the average amount of $j_\ast$ loss per merger event, we investigated the possibility that galaxy mergers are mainly responsible for the loss of angular momentum in higher density environments., Comment: 40 pages, 8 figures, 2 tables in the main text + appendix, published in MNRAS

We perform a kinematic and morphological analysis of 44 star-forming galaxies at $z\sim2$ in the COSMOS legacy field using near-infrared spectroscopy from Keck/MOSFIRE and F160W imaging from CANDELS/3D-HST as part of the ZFIRE survey. Our sample consists of cluster and field galaxies from $2.0 < z < 2.5$ with K band multi-object slit spectroscopic measurements of their H$\alpha$ emission lines. H$\alpha$ rotational velocities and gas velocity dispersions are measured using the Heidelberg Emission Line Algorithm (HELA), which compares directly to simulated 3D data-cubes. Using a suite of simulated emission lines, we determine that HELA reliably recovers input S$_{0.5}$ and angular momentum at small offsets, but $V_{2.2}/\sigma_g$ values are offset and highly scattered. We examine the role of regular and irregular morphology in the stellar mass kinematic scaling relations, deriving the kinematic measurement S$_{0.5}$, and finding $\log(S_{0.5}) = (0.38\pm0.07)\log(M/M_{\odot}-10) + (2.04\pm0.03)$ with no significant offset between morphological populations and similar levels of scatter ($\sim0.16$ dex). Additionally, we identify a correlation between M$_{\star}$ and $V_{2.2}/\sigma_g$ for the total sample, showing an increasing level of rotation dominance with increasing M$_{\star}$, and a high level of scatter for both regular and irregular galaxies. We estimate the specific angular momenta ($j_{disk}$) of these galaxies and find a slope of $0.36\pm0.12$, shallower than predicted without mass-dependent disk growth, but this result is possibly due to measurement uncertainty at M$_{\star}$ $<$ 9.5. However, through a K-S test we find irregular galaxies to have marginally higher $j_{disk}$ values than regular galaxies, and high scatter at low masses in both populations., Comment: Accepted to ApJ

We study the effects of galaxy environment on the evolution of the stellar-mass function (SMF) over 0.2 < z < 2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey and NEWFIRM Medium-Band Survey (NMBS) down to the stellar-mass completeness limit, log M / Msun > 9.0 (9.5) at z = 1.0 (2.0). We compare the SMFs for quiescent and star-forming galaxies in the highest and lowest environments using a density estimator based on the distance to the galaxies' third-nearest neighbors. For star-forming galaxies, at all redshifts there are only minor differences with environment in the shape of the SMF. For quiescent galaxies, the SMF in the lowest densities shows no evolution with redshift, other than an overall increase in number density (phi*) with time. This suggests that the stellar-mass dependence of quenching in relatively isolated galaxies is both universal and does not evolve strongly. While at z >~ 1.5 the SMF of quiescent galaxies is indistinguishable in the highest and lowest densities, at lower redshifts it shows a rapidly increasing number density of lower-mass galaxies, log M / Msun ~= 9-10. We argue this evolution can account for all the redshift evolution in the shape of the total quiescent-galaxy SMF. This evolution in the quiescent-galaxy SMF at higher redshift (z > 1) requires an environmental-quenching efficiency that decreases with decreasing stellar mass at 0.5 < z < 1.5 or it would overproduce the number of lower-mass quiescent galaxies in denser environments. This requires a dominant environment process such as starvation combined with rapid gas depletion and ejection at z > 0.5 - 1.0 for galaxies in our mass range. The efficiency of this process decreases with redshift allowing other processes (such as galaxy interactions and ram-pressure stripping) to become more important at later times, z < 0.5., Comment: Accepted for publication in the Astrophysical Journal, 19 pages

We investigate the relationship between the black hole accretion rate (BHAR) and star-formation rate (SFR) for Milky Way (MW) and Andromeda (M31)-mass progenitors from z = 0.2 - 2.5. We source galaxies from the Ks-band selected ZFOURGE survey, which includes multi-wavelenth data spanning 0.3 - 160um. We use decomposition software to split the observed SEDs of our galaxies into their active galactic nuclei (AGN) and star-forming components, which allows us to estimate BHARs and SFRs from the infrared (IR). We perform tests to check the robustness of these estimates, including a comparison to BHARs and SFRs derived from X-ray stacking and far-IR analysis, respectively. We find as the progenit- ors evolve, their relative black hole-galaxy growth (i.e. their BHAR/SFR ratio) increases from low to high redshift. The MW-mass progenitors exhibit a log-log slope of 0.64 +/- 0.11, while the M31-mass progenitors are 0.39 +/- 0.08. This result contrasts with previous studies that find an almost flat slope when adopting X-ray/AGN-selected or mass-limited samples and is likely due to their use of a broad mixture of galaxies with different evolutionary histories. Our use of progenitor-matched samples highlights the potential importance of carefully selecting progenitors when searching for evolutionary relationships between BHAR/SFRs. Additionally, our finding that BHAR/SFR ratios do not track the rate at which progenitors quench casts doubts over the idea that the suppression of star-formation is predominantly driven by luminous AGN feedback (i.e. high BHARs)., Comment: 7 pages, 5 figures, Accepted for publication in MNRAS

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 10^9 Msol. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct 3-dimensional density maps between 0.55

In this study we investigate 89 radio galaxies that are spectroscopically-confirmed to be members of five large scale structures in the redshift range of $0.65 \le z \le 0.96$. Based on a two-stage classification scheme, the radio galaxies are classified into three sub-classes: active galactic nucleus (AGN), hybrid, and star-forming galaxy (SFG). We study the properties of the three radio sub-classes and their global and local environmental preferences. We find AGN hosts are the most massive population and exhibit quiescence in their star-formation activity. The SFG population has a comparable stellar mass to those hosting a radio AGN but are unequivocally powered by star formation. Hybrids, though selected as an intermediate population in our classification scheme, were found in almost all analyses to be a unique type of radio galaxies rather than a mixture of AGN and SFGs. They are dominated by a high-excitation radio galaxy (HERG) population. We discuss environmental effects and scenarios for each sub-class. AGN tend to be preferentially located in locally dense environments and in the cores of clusters/groups, with these preferences persisting when comparing to galaxies of similar colour and stellar mass, suggesting that their activity may be ignited in the cluster/group virialized core regions. Conversely, SFGs exhibit a strong preference for intermediate-density global environments, suggesting that dusty starbursting activity in LSSs is largely driven by galaxy-galaxy interactions and merging., Comment: 28 pages, 10 figures, accepted to MNRAS

We study galactic star-formation activity as a function of environment and stellar mass over 0.59 (9.5)$ at z=1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision ($\sigma_z / (1+z) \lesssim 0.02$), recovers galaxies in low- and high-density environments accurately. We quantify the environmental quenching efficiency, and show that at z> 0.5 it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies ($\log (M/M_\odot)\gtrsim$ 10.5) at all redshifts. For lower mass galaxies ($\log (M/M)_\odot) \lesssim$ 10), the environmental quenching efficiency is very low at $z\gtrsim$ 1.5, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower mass galaxies ($\log(M/M_\odot) \sim$ 9-10), which appear primarily at $z\lesssim$ 1.0. The morphologies of lower mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star-formation and outflows ("overconsumption"), and additional processes such as galaxy interactions, tidal stripping and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations., Comment: 29 pages, 15 figure, accepted for publication in ApJ

We examine the effects of an impending cluster merger on galaxies in the large scale structure (LSS) RX J0910 at $z =1.105$. Using multi-wavelength data, including 102 spectral members drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey and precise photometric redshifts, we calculate star formation rates and map the specific star formation rate density of the LSS galaxies. These analyses along with an investigation of the color-magnitude properties of LSS galaxies indicate lower levels of star formation activity in the region between the merging clusters relative to the outskirts of the system. We suggest that gravitational tidal forces due to the potential of the merging halos may be the physical mechanism responsible for the observed suppression of star formation in galaxies caught between the merging clusters., Comment: 6 pages, 2 figures, 1 table, accepted in MNRAS Letters, v2 corrected a few typographical errors

We use the ZFIRE survey (http://zfire.swinburne.edu.au) to investigate the high mass slope of the initial mass function (IMF) for a mass-complete (log10(M$_*$/M$_\odot$)~9.3) sample of 102 star-forming galaxies at z~2 using their H$\alpha$ equivalent widths (H$\alpha$-EW) and rest-frame optical colours. We compare dust-corrected H$\alpha$-EW distributions with predictions of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic stellar population models. We find an excess of high H$\alpha$-EW galaxies that are up to 0.3--0.5 dex above the model-predicted Salpeter IMF locus and the H$\alpha$-EW distribution is much broader (10--500 \AA) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity, and the IMF upper-mass cutoff. IMF variations and/or highly rotating extreme metal poor stars (Z~0.1Z$_\odot$) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest H$\alpha$-EWs would require very shallow slopes ($\Gamma$>-1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z~2 show distinct differences from local populations and there is no simple physical model to explain the large variation in H$\alpha$-EWs at z~2., Comment: Accepted to MNRAS. 43 pages, 27 Figures. Survey website: http://zfire.swinburne.edu.au/

Using deep multi-wavelength photometry of galaxies from ZFOURGE, we group galaxies at $2.56$. Many of the EELGs also exhibit Lyman-$\alpha$ emission. Additionally, we find that many of these sources are clustered in an overdensity in the Chandra Deep Field South, with five spectroscopically confirmed members at $z=3.474 \pm 0.004$. The spatial distribution and photometric redshifts of the ZFOURGE population further confirm the overdensity highlighted by the EELGs., Comment: Accepted for publication in ApJL. 8 pages, 4 figures

We compare galaxy scaling relations as a function of environment at $z\sim2$ with our ZFIRE survey where we have measured H$\alpha$ fluxes for 90 star-forming galaxies selected from a mass-limited [$\log(M_{\star}/M_{\odot})>9$] sample based on ZFOURGE. The cluster galaxies (37) are part of a confirmed system at z=2.095 and the field galaxies (53) are at $1.92\times10^{11} L_{\odot}$). Because the LIRGs in our combined sample are $\sim5$ times more massive than the low-IR galaxies, their radii are $\sim70$% larger. To track stellar growth, we separate galaxies into those that lie above, on, and below the H$\alpha$ star-forming main sequence (SFMS) using $\Delta$SFR$(M_{\star})=\pm0.2$ dex. Galaxies above the SFMS (starbursts) tend to have higher H$\alpha$ SFR surface densities and younger light-weighted stellar ages compared to galaxies below the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field at $z\sim2$ are growing their stellar cores. Lastly, we compare to the (SFR-$M_{\star}$) relation from RHAPSODY cluster simulations and find the predicted slope is nominally consistent with the observations. However, the predicted cluster SFRs tend to be too low by a factor of $\sim2$ which seems to be a common problem for simulations across environment., Comment: ApJ in press; full version of Table 1 available from ApJ and upon request. Survey websites are http://zfire.swinburne.edu.au and http://zfourge.tamu.edu

The FourStar galaxy evolution survey (ZFOURGE) is a 45 night legacy program with the FourStar near-infrared camera on Magellan and one of the most sensitive surveys to date. ZFOURGE covers a total of $400\ \mathrm{arcmin}^2$ in cosmic fields CDFS, COSMOS and UDS, overlapping CANDELS. We present photometric catalogs comprising $>70,000$ galaxies, selected from ultradeep $K_s$-band detection images ($25.5-26.5$ AB mag, $5\sigma$, total), and $>80\%$ complete to $K_s<25.3-25.9$ AB. We use 5 near-IR medium-bandwidth filters ($J_1,J_2,J_3,H_s,H_l$) as well as broad-band $K_s$ at $1.05\ - 2.16\ \mu m$ to $25-26$ AB at a seeing of $\sim0.5$". Each field has ancillary imaging in $26-40$ filters at $0.3-8\ \mu m$. We derive photometric redshifts and stellar population properties. Comparing with spectroscopic redshifts indicates a photometric redshift uncertainty $\sigma_z={0.010,0.009}$, and 0.011 in CDFS, COSMOS, and UDS. As spectroscopic samples are often biased towards bright and blue sources, we also inspect the photometric redshift differences between close pairs of galaxies, finding $\sigma_{z,pairs}= 0.01-0.02$ at $1\times15$., Comment: 39 pages, 35 figures, accepted for publication in ApJ, full data release available at http://zfourge.tamu.edu/

In this study we present the exploration of $\sim$500 spectroscopically confirmed galaxies in and around two large scale structures at $z\sim1$ drawn from the ORELSE survey. A sub-sample of these galaxies ($\sim$150) were targeted for the initial phases of a near-infrared MOSFIRE spectroscopic campaign investigating the differences in selections of galaxies which had recently ended a burst of star formation or had rapidly quenched (i.e., post-starburst or K+A galaxies). Selection with MOSFIRE resulted in a post-starburst sample more than double that selected by traditional $z\sim1$ (observed-frame optical) methods even after the removal of the relatively large fraction of dusty starburst galaxies selected through traditional methods. While the traditional post-starburst fraction increased with increased global density, the MOSFIRE-selected post-starburst fraction was found to be constant in field, group, and cluster environments. However, this fraction relative to the number of galaxies with ongoing star formation was observed to elevate in the cluster environment. Post-starbursts selected with MOSFIRE were predominantly found to exhibit moderately strong [OII] emission originating from activity other than star formation. Such galaxies, termed K+A with ImposteR [OII]-derived Star formation (KAIROS) galaxies, were found to be considerably younger than traditionally-selected post-starbursts and likely undergoing some form of feedback absent or diminished in traditional post-starbursts. A comparison between the environments of the two types of post-starbursts suggests a picture in which the evolution of a post-starburst galaxy is considerably different in cluster environments than in the more rarefied environments of a group or the field., Comment: 20 pages, seven figures, four tables, accepted to MNRAS after minor changes to v1, v3 fixes a rendering issue present in v2

We present an overview and the first data release of ZFIRE, a spectroscopic redshift survey of star-forming galaxies that utilizes the MOSFIRE instrument on Keck-I to study galaxy properties in rich environments at $1.5

We investigate the star formation rate (SFR) dependence on the stellar mass and gas-phase metallicity relation at z=2 with MOSFIRE/Keck as part of the ZFIRE survey. We have identified 117 galaxies (1.98 < z < 2.56), with $8.9\leq$log(M/M$_{\odot}$)$\leq11.0$, for which we can measure gas-phase metallicities. For the first time, we show discernible difference between the mass-metallicity relation, using individual galaxies, when deviding the sample by low ($<10$~M$_{\odot}$yr$^{-1}$) and high ($>10$~M$_{\odot}$yr$^{-1}$) SFRs. At fixed mass, low star-forming galaxies tend to have higher metallicity than high star-forming galaxies. Using a few basic assumptions, we further show that the gas masses and metallicities required to produce the fundamental mass--metallicity relation, and its intrinsic scatter, are consistent with cold-mode accretion predictions obtained from the OWLS hydrodynamical simulations. Our results from both simulations and observations are suggestive that cold-mode accretion is responsible for the fundamental mass-metallicity relation at $z=2$ and demonstrates the direct relationship between cosmological accretion and the fundamental properties of galaxies., Comment: 6 pages, 3 figures; accepted for publication in ApJ Letters

We perform a kinematic analysis of galaxies at $z\sim2$ in the COSMOS legacy field using near-infrared (NIR) spectroscopy from Keck/MOSFIRE as part of the ZFIRE survey. Our sample consists of 75 Ks-band selected star-forming galaxies from the ZFOURGE survey with stellar masses ranging from log(M$_{\star}$/M$_{\odot}$)$=9.0-11.0$, 28 of which are members of a known overdensity at $z=2.095$. We measure H$\alpha$ emission-line integrated velocity dispersions ($\sigma_{\rm int}$) from 50$-$230 km s$^{-1}$, consistent with other emission-line studies of $z\sim2$ field galaxies. From these data we estimate virial, stellar, and gas masses and derive correlations between these properties for cluster and field galaxies at $z\sim2$. We find evidence that baryons dominate within the central effective radius. However, we find no statistically significant differences between the cluster and the field, and conclude that the kinematics of star-forming galaxies at $z\sim2$ are not significantly different between the cluster and field environments., Comment: 6 pages, 4 figures, accepted for publication in ApJL

We build a set of composite galaxy SEDs by de-redshifting and scaling multi-wavelength photometry from galaxies in the ZFOURGE survey, covering the CDFS, COSMOS, and UDS fields. From a sample of ~4000 K_s-band selected galaxies, we define 38 composite galaxy SEDs that yield continuous low-resolution spectra (R~45) over the rest-frame range 0.1-4 um. Additionally, we include far infrared photometry from the Spitzer Space Telescope and the Herschel Space Observatory to characterize the infrared properties of our diverse set of composite SEDs. From these composite SEDs we analyze the rest-frame UVJ colors, as well as the ratio of IR to UV light (IRX) and the UV slope ($\beta$) in the IRX$-\beta$ dust relation at 1

We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star-formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep $K_{s}$-band imaging of ZFOURGE with overlapping multi-wavelength data. From this, we construct a mass-complete (log(M$_{*}$/M$_{\odot}$) $\ge$ 9.75), AGN luminosity limited sample of 235 AGN hosts over z = 0.2 - 3.2. We compare the rest-frame U - V versus V - J (UVJ) colours and specific star-formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160{\mu}m Herschel PACS data, we find the mean specific star-formation rate of AGN hosts to be elevated by 0.34$\pm$0.07 dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ~5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested., Comment: 15 pages, 9 figures, Accepted for publication in MNRAS

We measure the evolution of the quiescent fraction and quenching efficiency of satellites around star-forming and quiescent central galaxies with stellar mass $\log(M_{\mathrm{cen}}/M_{\odot})>10.5$ at $0.39.3$. Satellites for both star-forming and quiescent central galaxies have higher quiescent fractions compared to field galaxies matched in stellar mass at all redshifts. We also observe "galactic conformity": satellites around quiescent centrals are more likely to be quenched compared to the satellites around star-forming centrals. In our sample, this conformity signal is significant at $\gtrsim3\sigma$ for $0.6

We explore star-formation histories (SFHs) of galaxies based on the evolution of the star-formation rate stellar mass relation (SFR-M*). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M* relation at 0.5 < z < 4. Similar to recent works we find that the average infrared SEDs of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that the SFR-M* relation is not consistent with a single power-law of the form SFR ~ M*^a at any redshift; it has a power-law slope of a~1 at low masses, and becomes shallower above a turnover mass (M_0) that ranges from 10^9.5 - 10^10.8 Msol, with evidence that M_0 increases with redshift. We compare our measurements to results from state-of-the-art cosmological simulations, and find general agreement in the slope of the SFR-M* relation albeit with systematic offsets. We use the evolving SFR-M* sequence to generate SFHs, finding that typical SFRs of individual galaxies rise at early times and decline after reaching a peak. This peak occurs earlier for more massive galaxies. We integrate these SFHs to generate mass-growth histories and compare to the implied mass-growth from the evolution of the stellar mass function. We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass-growth rates that are as much as 10x higher than inferred from the stellar mass function. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers., Comment: Accepted for publication in the ApJ: 16 pages, 11 figures, 1 table

We spectroscopically survey the galaxy cluster XMM-LSS J02182-05102 (hereafter IRC 0218) using LRIS (optical) and MOSFIRE (near-infrared) on Keck I as part of the ZFIRE survey. IRC 0218 has a narrow redshift range of $1.612

We investigate the ISM properties of 13 star-forming galaxies within the z~2 COSMOS cluster. We show that the cluster members have [NII]/Ha and [OIII]/Hb emission-line ratios similar to z~2 field galaxies, yet systematically different emission-line ratios (by ~0.17 dex) from the majority of local star-forming galaxies. We find no statistically significant difference in the [NII]/Ha and [OIII]/Hb line ratios or ISM pressures among the z~2 cluster galaxies and field galaxies at the same redshift. We show that our cluster galaxies have significantly larger ionization parameters (by up to an order of magnitude) than local star-forming galaxies. We hypothesize that these high ionization parameters may be associated with large specific star formation rates (i.e. a large star formation rate per unit stellar mass). If this hypothesis is correct, then this relationship would have important implications for the geometry and/or the mass of stars contained within individual star clusters as a function of redshift., Comment: 11 pages, 5 figures, accepted for publication in ApJ

We study the rest-frame ultra-violet sizes of massive (~0.8 x 10^11 M_Sun) galaxies at 3.45 x, between 2

There is ongoing debate regarding the extent that environment affects galaxy size growth beyond z>1. To investigate the differences in star-forming and quiescent galaxy properties as a function of environment at z=2.1, we create a mass-complete sample of 59 cluster galaxies Spitler et al. (2012) and 478 field galaxies with log(M)>9 using photometric redshifts from the ZFOURGE survey. We compare the mass-size relation of field and cluster galaxies using measured galaxy semi-major axis half-light radii ($r_{1/2,maj}$) from CANDELS HST/F160W imaging. We find consistent mass normalized (log(M)=10.7) sizes for quiescent field galaxies ($r_{1/2,maj}=1.81\pm0.29$ kpc) and quiescent cluster galaxies ($r_{1/2,maj}=2.17\pm0.63$ kpc). The mass normalized size of star-forming cluster galaxies ($r_{1/2,maj}=4.00\pm0.26$ kpc ) is 12% larger (KS test $2.1\sigma$) than star-forming field galaxies ($r_{1/2,maj}=3.57\pm0.10$ kpc). From the mass-color relation we find that quiescent field galaxies with 9.710.4 have consistent colors. We find that star-forming cluster galaxies are on average 20% redder than star-forming field galaxies at all masses. Furthermore, we stack galaxy images to measure average radial color profiles as a function of mass. Negative color gradients are only present for massive star-forming field and cluster galaxies with log(M)>10.4, the remaining galaxy masses and types have flat profiles. Our results suggest given the observed differences in size and color of star-forming field and cluster galaxies, that the environment has begun to influence/accelerate their evolution. However, the lack of differences between field and cluster quiescent galaxies indicates that the environment has not begun to significantly influence their evolution at z~2., Comment: 11 pages, 8 figures, accepted by ApJ. Information on ZFOURGE can be found at http://zfourge.tamu.edu

We investigate the environmental dependence of the mass-metallicity relation at z=2 with MOSFIRE/Keck as part of the ZFIRE survey. Here, we present the chemical abundance of a Virgo-like progenitor at z=2.095 that has an established red sequence. We identified 43 cluster ($=2.095\pm0.004$) and 74 field galaxies ($=2.195\pm0.083$) for which we can measure metallicities. For the first time, we show that there is no discernible difference between the mass-metallicity relation of field and cluster galaxies to within 0.02dex. Both our field and cluster galaxy mass-metallicity relations are consistent with recent field galaxy studies at z~2. We present hydrodynamical simulations for which we derive mass-metallicity relations for field and cluster galaxies. We find at most a 0.1dex offset towards more metal-rich simulated cluster galaxies. Our results from both simulations and observations are suggestive that environmental effects, if present, are small and are secondary to the ongoing inflow and outflow processes that are governed by galaxy halo mass., Comment: 5 pages, 3 figures; accepted for publication in ApJ Letters

We present the spectroscopic confirmation of a galaxy cluster at $z=2.095$ in the COSMOS field. This galaxy cluster was first reported in the ZFOURGE survey as harboring evolved massive galaxies using photometric redshifts derived with deep near-infrared (NIR) medium-band filters. We obtain medium resolution ($R \sim$ 3600) NIR spectroscopy with MOSFIRE on the Keck 1 telescope and secure 180 redshifts in a $12'\times12'$ region. We find a prominent spike of 57 galaxies at $z=2.095$ corresponding to the galaxy cluster. The cluster velocity dispersion is measured to be $\sigma_{\rm v1D}$ = 552 $\pm$ 52 km/s. This is the first study of a galaxy cluster in this redshift range ($z \gt 2.0$) with the combination of spectral resolution ($\sim$26 km/s) and the number of confirmed members (${>}50$) needed to impose a meaningful constraint on the cluster velocity dispersion and map its members over a large field of view. Our $\Lambda$CDM cosmological simulation suggests that this cluster will most likely evolve into a Virgo-like cluster with ${\rm M_{vir}}{=}10^{14.4\pm0.3} {\rm M_\odot}$ ($68\%$ confidence) at $z\sim$ 0. The theoretical expectation of finding such a cluster is $\sim$ $4\%$. Our results demonstrate the feasibility of studying galaxy clusters at $z > 2$ in the same detailed manner using multi-object NIR spectrographs as has been done in the optical in lower redshift clusters., Comment: 6 pages, 5 figures; accepted for publication in ApJ Letters

We study the statistical distribution of satellites around star-forming and quiescent central galaxies at 19$ at z<3. The radial satellite distribution around centrals is consistent with a projected NFW profile. Massive quiescent centrals, $\log(M/M_\odot)>10.78$, have $\sim$2 times the number of satellites compared to star-forming centrals with a significance of 2.7$\sigma$ even after accounting for differences in the centrals' stellar-mass distributions. We find no statistical difference in the satellite distributions of intermediate-mass quiescent and star-forming centrals, $10.48<\log(M/M_\odot)<10.78$. Comparing to the Guo2011 semi-analytic model, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than star-forming centrals, even when the stellar-mass distributions are fixed. We use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between star-forming and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from $\sim$0 for $\log(M_h/M_\odot)\sim$11 to $\sim$1 for $\log(M_h/M_\odot)\sim$13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive halos., Comment: 19 pages, 17 figures, accepted by ApJ. Information on ZFOURGE can be found at http://zfourge.tamu.edu

Our understanding of the redshift $z>3$ galaxy population relies largely on samples selected using the popular "dropout" technique, typically consisting of UV-bright galaxies with blue colors and prominent Lyman breaks. As it is currently unknown if these galaxies are representative of the massive galaxy population, we here use the FourStar Galaxy Evolution (ZFOURGE) Survey to create a stellar mass-limited sample at $z=3-4$. Uniquely, ZFOURGE uses deep near-infrared medium-bandwidth filters to derive accurate photometric redshifts and stellar population properties. The mass-complete sample consists of 57 galaxies with log M $>10.6$, reaching below $M^{\star}$ at $z=3-4$. On average, the massive $z=3-4$ galaxies are extremely faint in the observed optical with median $R_{tot}^{AB}=27.48\pm0.41$ (restframe $M_{1700}=-18.05\pm0.37$). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about $\sim100\times$ fainter at the same mass. The massive galaxies are red ($R-Ks_{AB}=3.9\pm0.2$; restframe UV-slope $\beta=-0.2\pm0.3$) likely from dust or old stellar ages. We classify the galaxy SEDs by their restframe $U-V$ and $V-J$ colors and find a diverse population: $46^{+6+10}_{-6-17}$% of the massive galaxies are quiescent, $54^{+8+17}_{-8-10}$% are dusty star-forming galaxies, and only $14^{+3+10}_{-3-4}$% resemble luminous blue star forming Lyman break galaxies. This study clearly demonstrates an inherent diversity among massive galaxies at higher redshift than previously known. Furthermore,we uncover a reservoir of dusty star-forming galaxies with $4\times$ lower specific star-formation rates compared to submillimeter-selected starbursts at $z>3$. With $5\times$ higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts., Comment: Accepted for publication in ApJ Letters. See http://zfourge.tamu.edu for more details about ZFOURGE

We report the likely identification of a substantial population of massive M~10^11M_Sun galaxies at z~4 with suppressed star formation rates (SFRs), selected on rest-frame optical to near-IR colors from the FourStar Galaxy Evolution Survey. The observed spectral energy distributions show pronounced breaks, sampled by a set of near-IR medium-bandwidth filters, resulting in tightly constrained photometric redshifts. Fitting stellar population models suggests large Balmer/4000AA breaks, relatively old stellar populations, large stellar masses and low SFRs, with a median specific SFR of 2.9+/-1.8 x 10^-11/yr. Ultradeep Herschel/PACS 100micron, 160micron and Spitzer/MIPS 24micron data reveal no dust-obscured SFR activity for 15/19 (79%) galaxies. Two far-IR detected galaxies are obscured QSOs. Stacking the far-IR undetected galaxies yields no detection, consistent with the SED fit, indicating independently that the average specific SFR is at least 10x smaller than of typical star-forming galaxies at z~4. Assuming all far-IR undetected galaxies are indeed quiescent, the volume density is 1.8+/-0.7 x 10^-5Mpc^-3 to a limit of log10M/M_Sun>10.6, which is 10x and 80x lower than at z = 2 and z = 0.1. They comprise a remarkably high fraction (~35%) of z~4 massive galaxies, suggesting that suppression of star formation was efficient even at very high redshift. Given the average stellar age of 0.8Gyr and stellar mass of 0.8x10^11M_Sun, the galaxies likely started forming stars before z =5, with SFRs well in excess of 100M_Sun/yr, far exceeding that of similarly abundant UV-bright galaxies at z>4. This suggests that most of the star-formation in the progenitors of quiescent z~4 galaxies was obscured by dust., Comment: 8 pages, 4 figures, 1 table, accepted by ApjL

Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function at 0.5 < z < 2.5. ZFOURGE provides well-constrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2um . We combine this with HST imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS), allowing for the efficient selection of both blue and red galaxies down to stellar masses ~10^9.5 Msol at z ~ 2.5. The total surveyed area is 316 arcmin^2 distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey (NMBS) to provide stronger constraints at high masses. Several studies at z<=1 have revealed a steepening of the slope at the low-mass end of the stellar mass function (SMF), leading to an upturn at masses <10^10 Msol that is not well-described by a standard single-Schechter function. We find evidence that this feature extends to at least z ~ 2, and that it can be found in both the star-forming and quiescent populations individually. The characteristic mass (M*) and slope at the lowest masses (alpha) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/Msol) ~ 10.65 and ~-1.5 respectively. The SMF of star-forming galaxies has evolved primarily in normalization, while the change in shape is relatively minor. This is not the case for quiescent galaxies: the depth of our imaging allows us to show for the first time significantly more evolution at Log(M/Msol) < 10.5 than at higher masses. We find that the total mass density (down to 10^9 Msol) in star-forming galaxies has increased by a factor of ~2.2 since z ~ 2.5, whereas in quiescent galaxies it has increased by a factor of ~12 ., Comment: 17 pages, 13 figures. Accepted for publication in the ApJ

We conduct a deep mid-infrared census of nine massive galaxy clusters at (03 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame V(AB) magnitude <-21.5 and (2) mid-IR selected members brighter than (M*+0.5), i.e. essentially a stellar mass cut. In both samples, we measure \agnfrac ~1% with a strong upper limit of ~3% at z<1. This uniformly low IR-AGN fraction at z<1 is surprising given the fraction of 24 micron sources in the same galaxy clusters is observed to increase by about a factor of four from z~0 to z~1; this indicates that most of the detected 24 micron flux is due to star formation. Only in our single galaxy cluster at z=1.24 is the IR-AGN fraction measurably higher at ~15% (all members; ~70% for late-types only). In agreement with recent studies, we find the cluster IR-AGN are predominantly hosted by late-type galaxies with blue optical colors, i.e. members with recent/ongoing star formation. The four brightest IR-AGN are also X-ray sources; these IR+X-ray AGN all lie outside the cluster core (Rproj>0.5 Mpc) and are hosted by highly morphologically disturbed members. Although our sample is limited, our results suggest that \agnfrac in massive galaxy clusters is not strongly correlated with star formation at z<1, and that IR-AGN have a more prominent role at z>1., Comment: 13 pages, 8 figures, accepted to the Astrophysical Journal