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CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies
Guo, Yicheng,Bell, Eric F.,Lu, Yu,Koo, David C.,Faber, S. M.,Koekemoer, Anton M.,Kurczynski, Peter,Lee, Seong-Kook,Papovich, Casey,Chen, Zhu,Dekel, Avishai,Ferguson, Henry C.,Fontana, Adriano,Giavalis American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.841 No.2
<P>We investigate the environmental quenching of galaxies, especially those with stellar masses (M-*) < 10(9.5) Me-circle dot, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z greater than or similar to 1.5. For each low-mass galaxy, we measure the projected distance (d(proj)) to its nearest massive neighbor (M-* > 10(10.5) M-circle dot) within a redshift range. At a given z and M-*, the environmental quenching effect is considered to be observed if the d(proj) distribution of QGs (d(proj)(Q)) is significantly skewed toward lower values than that of star-forming galaxies (d(proj)(SF)). For galaxies with 10(8) M-circle dot < M-* < 10(10) M-circle dot, such a difference between d(proj)(Q) and d(proj)(SF) is detected up to z similar to 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (R-Vir) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, d(proj)(Q)/R-Vir, decreases with satellite M-* at M-* less than or similar to 10(9.5) M-circle dot, but increases with satellite M-* at M-* greater than or similar to 10(9.5) M-circle dot. This trend suggests a smooth, if any, transition of the quenching timescale around M-* similar to 10(9.5) M-circle dot at 0.5 < z < 1.0.</P>
Song, Mimi,Finkelstein, Steven L.,Ashby, Matthew L. N.,Grazian, A.,Lu, Yu,Papovich, Casey,Salmon, Brett,Somerville, Rachel S.,Dickinson, Mark,Duncan, K.,Faber, Sandy M.,Fazio, Giovanni G.,Ferguson, He American Astronomical Society 2016 The Astrophysical Journal Vol.825 No.1
<P>We present galaxy stellar mass functions (GSMFs) at z = 4-8 from a rest-frame ultraviolet (UV) selected sample of similar to 4500 galaxies, found via photometric redshifts over an area of similar to 280 arcmin(2) 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 angstrom (M-UV) and logarithmic stellar mass (log M-*) that holds for galaxies with log(M-*/M-circle dot) less than or similar to 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 alpha = -1.55(-0.07)(+0.08) at z = 4 to alpha = -2.25(-0.35)(+0.72) at z = 8. The inferred stellar mass density, when integrated over M-* = 10(8)-10(13) M-circle dot, 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.</P>