2016ApJ...825....5S

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 arcmin² in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Great Observatories Origins Deep Survey (GOODS) fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data to date and the relatively large volume allow us to place a better constraint at both the low- and 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 rest-frame UV absolute magnitude at 1500 Å ( {M}_{UV} ) and logarithmic stellar mass ( log{M}_{* } ) that holds for galaxies with log({M}_{* }/{M}_☉)\lesssim 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}_{-0.07}^{+0.08} at z=4 to α=-{2.25}_{-0.35}^{+0.72} at z=8. The inferred stellar mass density, when integrated over {M}_{* }={10}^{8} -10¹³ M_☉, increases by a factor of {10}_{-2}^{+30} between z=7 and z=4 and is in good agreement with the time integral of the cosmic star formation rate density.