Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function at 0.2 < z < 3. ZFOURGE provides wellconstrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2µm. 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 M ⊙ 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 ≤ 1.5 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 M ⊙ 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 (α) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/M ⊙ ) ∼ 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. Our data allow us for the first time to observe a rapid buildup at the low-mass end of the quiescent SMF. Since z = 2.5, the total stellar mass density of quiescent galaxies (down to 10 9 M ⊙ ) has increased by a factor of ∼12 whereas the mass density of star-forming galaxies only increases by a factor of ∼2.2. * This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

We study galactic star-formation activity as a function of environment and stellar mass over 0.5 9 (9.5) at z=1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision (σ z /(1 + z) 0.02) of ZFOURGE, 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 ⊙ ) 10.5) at all redshifts. For lower mass galaxies (log(M/M ) ⊙ ) 10), the environmental quenching efficiency is very low at z 1.5, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower mass galaxies (log(M/M ⊙ ) ∼ 9-10), which appear primarily at z 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, tidalCorresponding author: Lalitwadee Kawinwanichakij kawinwanichakij@physics.tamu.edu * This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. 2 stripping, and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.

We present the results from a new search for candidate galaxies at z ≈ 8.5–11 discovered over the 850 arcmin2 area probed by the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). We use a photometric-redshift selection including both Hubble and Spitzer Space Telescope photometry to robustly identify galaxies in this epoch at H 160 < 26.6. We use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up Hubble Space Telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. The inclusion of Spitzer/IRAC photometry in the selection process reduces contamination, and yields more robust redshift estimates than Hubble alone. We constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. We find that the abundance at our brightest probed luminosities (M UV = − 22.3) is consistent with predictions from simulations that assume that galaxies in this epoch have gas depletion times at least as short as those in nearby starburst galaxies. Due to large Poisson and cosmic variance uncertainties, we cannot conclusively rule out either a smooth evolution of the luminosity function continued from z = 4–8, or an accelerated decline at z > 8. We calculate that the presence of seven galaxies in a single field Extended Groth Strip is an outlier at the 2σ significance level, implying the discovery of a significant over-density. These scenarios will be imminently testable to high confidence within the first year of observations of the James Webb Space Telescope.

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 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, 5σ, 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 µm to 25 − 26 AB at a seeing of ∼ 0.′′ 5. Each field has ancillary imaging in 26 − 40 filters at 0.3 − 8 µm. We derive photometric redshifts and stellar population properties. Comparing with spectroscopic redshifts indicates a photometric redshift uncertainty σ 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 σ z,pairs = 0.01 − 0.02 at 1 < z < 2.5. We quantify how σ z,pairs depends on redshift, magnitude, SED type, and the inclusion of FourStar medium bands. σ z,pairs is smallest for bright, blue star-forming samples, while red starforming galaxies have the worst σ z,pairs . Including FourStar medium bands reduces σ z,pairs by 50% at 1.5 < z < 2.5. We calculate SFRs based on ultraviolet and ultradeep far-IR Spitzer/MIPS and Herschel/PACS data. We derive rest-frame U − V and V − J colors, and illustrate how these correlate with specific SFR and dust emission to z = 3.5. We confirm the existence of quiescent galaxies at z ∼ 3, demonstrating their SFRs are suppressed by > ×15.

Galaxies with stellar masses near M * contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present-day stellar masses near M * , at 5 × 10 10 M (defined here to be MW-mass) and 10 11 M (defined to be M31-mass). We study the typical progenitors of these galaxies using the FourStar Galaxy Evolution Survey (ZFOURGE). ZFOURGE is a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z ∼ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star formation rates, combining our deep multiwavelength imaging with near-IR Hubble Space Telescope imaging from Cosmic Near-IR Deep Extragalactic Legacy Survey (CANDELS), and Spitzer and Herschel far-IR imaging from Great Observatories Origins Deep Survey-Herschel and CANDELS-Herschel. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages to redder dust-obscured IR-luminous galaxies in intermediate stages and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of two to three lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star formation in present-day M * galaxies, requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and SFRs imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z ∼ 0 and are strongly anticorrelated with an increase in the Sérsic index. Therefore, the growth of galaxy bulges in M * galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star formation efficiency.

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 * /M ⊙ > 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 (φ * ) 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 * /M ⊙ ≃ 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.

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 at z = 3 − 4.On average, the massive z = 3 − 4 galaxies are extremely faint in the observed optical with median R AB tot = 27.48 ± 0.41 (restframe M 1700 = −18.05 ± 0.37). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about ∼ 100× fainter at the same mass. The massive galaxies are red (R − Ks AB = 3.9 ± 0.2; restframe UV-slope β = −0.2 ± 0.3) 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, 40 +6+7 −6−5 % 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× lower specific starformation rates compared to submillimeter-selected starbursts at z > 3. With 5× higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts.

We present post-cryogenic Spitzer imaging at 3.6 and 4.5 µm with the Infrared Array Camera (IRAC) of the Spitzer/HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ≈24 deg 2 of the Sloan Digital Sky Survey "Stripe 82" region, and falls within the footprints of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R ∼ 800 spectroscopy will produce ∼ 200,000 redshifts from the Lyman-α emission for galaxies in the range 1.9 < z < 3.5, and an additional ∼ 200,000 redshifts from the [O II] emission for galaxies at z < 0.5. When combined with deep ugriz images from the Dark Energy Camera, K-band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, AGN, and environment over a co-moving volume of ∼0.5 Gpc 3 at 1.9 < z < 3.5. Here, we discuss the properties of the SHELA IRAC dataset, including the data acquisition, reduction, validation, and source catalogs. Our tests show the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 µm images. The catalogs reach limiting sensitivities of 1.1 µJy at both 3.6 and 4.5 µm (1σ, for R = 2 ′′ circular apertures). As a demonstration of science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of Spitzer Exploratory programs we provide all images and catalogs as part of the publication.