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.

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.

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.