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We present galaxy stellar mass functions (GSMFs) at z = 4-8 from a rest-frame ultraviolet (UV) selected sample of ∼4500 galaxies, found via photometric redshifts over an area of ∼280 arcmin 2 in the CANDELS/GOODS fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data yet-to-date and the relatively large volume allow us to place a better constraint at both the lowand high-mass ends of the GSMFs compared to previous space-based studies from pre-CANDELS observations. Supplemented by a stacking analysis, we find a linear correlation between the restframe UV absolute magnitude at 1500Å (M UV ) and logarithmic stellar mass (log M * ) that holds for galaxies with log(M * /M ) 10. We use simulations to validate our method of measuring the slope of the log M * -M UV relation, finding that the bias is minimized with a hybrid technique combining photometry of individual bright galaxies with stacked photometry for faint galaxies. The resultant measured slopes do not significantly evolve over z = 4-8, while the normalization of the trend exhibits a weak evolution toward lower masses at higher redshift. We combine the log M * -M UV distribution with observed rest-frame UV luminosity functions at each redshift to derive the GSMFs, finding that the low-mass-end slope becomes steeper with increasing redshift from α = −1.55 +0.08 −0.07 at z = 4 to α = −2.25 +0.72 −0.35 at z = 8. The inferred stellar mass density, when integrated over M * = 10 8 -10 13 M , increases by a factor of 10 +30 −2 between z = 7 and z = 4 and is in good agreement with the time integral of the cosmic star formation rate density. HST Data and Sample SelectionThe galaxy sample employed in this study is from Finkelstein et al. (2015), to which we refer the reader for full details of the HST data used and the galaxy sample selection. This sample consists of ∼7000 galaxies selected via photometric redshifts over a redshift range of z = 3.5-8.5. These galaxies were selected using HST

We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Nearinfrared Deep Extragalactic Legacy Survey (CANDELS) project. We combine the effort from ten different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age < 100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for < 20 Myr sources) if nebular contribution is ignored.

Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at < < z 0.2 2.1. A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Lowmass galaxies ( * M M log 9.5 ( ) ) grow on average slowly, take a long time to reach their peak of star formation (4 Gyr), and then the declining phase is fast (2 Gyr). Conversely, high-mass galaxies ( * M M log 11 ( ) ) grow on average fast (2 Gyr), and, after reaching their peak, decrease the star formation slowly (3). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with highmass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low-and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.

We use the deepest and the most comprehensive photometric data currently available for GOODS-South (GOODS-S) galaxies to measure their photometric redshifts. The photometry includes VLT/VIMOS (U band), HST /ACS (F435W, F606W, F775W, and F850LP bands), VLT/ISAAC (J, H, and K s bands), and four Spitzer/IRAC channels (3.6, 4.5, 5.8, and 8.0µm). The catalog is selected in the z band (F850LP) and photometry in each band is carried out using the recently completed TFIT algorithm, which performs point-spread function (PSF) matched photometry uniformly across different instruments and filters, despite large variations in PSFs and pixel scales. Photometric redshifts are derived using the GOODZ code, which is based on the template fitting method using priors. The code also implements "training" of the template spectral energy distribution (SED) set, using available spectroscopic redshifts in order to minimize systematic differences between the templates and the SEDs of the observed galaxies. Our final catalog covers an area of 153 arcmin 2 and includes photometric redshifts for a total of 32,505 objects. The scatter between our estimated photometric and spectroscopic redshifts is σ=0.040 with 3.7% outliers to the full z-band -2depth of our catalog, decreasing to σ=0.039 and 2.1% outliers at a magnitude limit m z <24.5. This is consistent with the best results previously published for GOODS-S galaxies, however, the present catalog is the deepest yet available and provides photometric redshifts for significantly more objects to deeper flux limits and higher redshifts than earlier works. Furthermore, we show that the photometric redshifts estimated here for galaxies selected as dropouts are consistent with those expected based on the Lyman break technique.