The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift

摘要: We present galaxy stellar mass functions (GSMFs) at $z=$ 4-8 from a rest-frame ultraviolet (UV) selected sample of $\sim$4500 galaxies, found via photometric redshifts over an area $\sim$280 arcmin$^2$ in the CANDELS/GOODS fields and Hubble Ultra Deep Field. The deepest Spitzer/IRAC data yet-to-date relatively large volume allow us to place better constraint both low- high-mass ends GSMFs compared previous space-based studies pre-CANDELS observations. Supplemented by stacking analysis, we find linear correlation between UV absolute magnitude 1500 A ($M_{\rm UV}$) logarithmic ($\log M_*$) that holds for galaxies with $\log(M_*/M_{\odot}) \lesssim 10$. use simulations validate our method measuring slope $\log M_*$-$M_{\rm UV}$ relation, finding bias is minimized hybrid technique combining photometry individual bright stacked faint galaxies. resultant measured slopes do not significantly evolve 4-8, while normalization trend exhibits weak evolution toward lower masses higher redshift. combine distribution observed luminosity each redshift derive GSMFs, low-mass-end becomes steeper increasing $\alpha=-1.55^{+0.08}_{-0.07}$ $z=4$ $\alpha=-2.25^{+0.72}_{-0.35}$ $z=8$. inferred density, when integrated $M_*=10^8$-$10^{13} M_{\odot}$, increases factor $10^{+30}_{-2}$ $z=7$ good agreement time integral cosmic star formation rate density.