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 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 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 \AA\ (MUV) and logarithmic stellar mass
(logM∗) that holds for galaxies with log(M∗/M⊙)≲10. We
use simulations to validate our method of measuring the slope of the logM∗-MUV 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 logM∗-MUV 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∗=108-1013M⊙, 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.Comment: 27 pages, 17 figures, ApJ, in pres