THE EVOLUTION OF THE GALAXY STELLAR MASS FUNCTION AT z=4-8: A STEEPENING LOW-MASS-END SLOPE WITH INCREASING REDSHIFT
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ABSTRACTWe present galaxy stellar mass functions (GSMFs) at z = 48 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 ( m{UV}}}$?> ) and logarithmic stellar mass () that holds for galaxies with . We use simulations to validate our method of measuring the slope of the 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 = 48, while the normalization of the trend exhibits a weak evolution toward lower masses at higher redshift. We combine the 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 at z = 4 to at z = 8. The inferred stellar mass density, when integrated over 1013M, increases by a factor of between z = 7 and z = 4 and is in good agreement with the time integral of the cosmic star formation rate density.
