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SATELLITE QUENCHING AND GALACTIC CONFORMITY AT 0.3 <<i>z</i>< 2.5
Kawinwanichakij, Lalitwadee,Quadri, Ryan F.,Papovich, Casey,Kacprzak, Glenn G.,Labbé,, Ivo,Spitler, Lee R.,Straatman, Caroline M. S.,Tran, Kim-Vy H.,Allen, Rebecca,Behroozi, Peter,Cowley, Michae American Astronomical Society 2016 The Astrophysical journal Vol.817 No.1
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>
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>
DISCOVERY OF A STRONG LENSING GALAXY EMBEDDED IN A CLUSTER AT z = 1.62
WONG, KENNETH C.,TRAN, KIM-VY H.,SUYU, SHERRY H.,MOMCHEVA, IVELINA G.,BRAMMER, GABRIEL B.,BRODWIN, MARK,GONZALEZ, ANTHONY H.,HALKOLA, ALEKSI,KACPRZAK, GLENN G.,KOEKEMOER, ANTON M.,PAPOVICH, CASEY J.,R The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We identify a strong lensing galaxy in the cluster IRC 0218 that is spectroscopically confirmed to be at z = 1.62, making it the highest-redshift strong lens galaxy known. The lens is one of the two brightest cluster galaxies and lenses a background source galaxy into an arc and a counterimage. With Hubble Space Telescope (HST) grism and Keck/LRIS spectroscopy, we measure the source redshift to be $z_S=2.26$. Using HST imaging, we model the lens mass distribution with an elliptical power-law profile and account for the effects of the cluster halo and nearby galaxies. The Einstein radius is $^{\theta}E=0.38^{+0.02{\prime}{\prime}}_{-0.01}$ ($3.2^{+0.2}_{-0.1}kpc$) and the total enclosed mass is $M_{tot}(<^{\theta}_E)=1.8^{+0.2}_{-0.1}{\times}10^{11}M_{\odot}$. We estimate that the cluster environment contributes ~ 10% of this total mass. Assuming a Chabrier IMF, the dark matter fraction within $^{\theta}E$ is $f^{Chab}_{DM}=0.3^{+0.1}_{-0.3}$, while a Salpeter IMF is marginally inconsistent with the enclosed mass ($f^{Salp}_{DM}=-0.3^{+0.2}_{-0.5}$).
Ko, Jongwan,Im, Myungshin,Lee, Hyung Mok,Lee, Myung Gyoon,Kim, Seong Jin,Shim, Hyunjin,Jeon, Yiseul,Hwang, Ho Seong,Willmer, Christopher N. A.,Malkan, Matthew A.,Papovich, Casey,Weiner, Benjamin J.,Ma IOP Publishing 2012 The Astrophysical journal Vol.745 No.2
<P>We present the mid-infrared (MIR) properties of galaxies within a supercluster in the north ecliptic pole region at z similar to 0.087 observed with the AKARI satellite. We use data from the AKARI NEP-Wide (5.4 deg(2)) IR survey and the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show that near-IR (3 mu m)-mid-IR (11 mu m) color can be used as an indicator of the specific star formation rate and the presence of intermediate-age stellar populations. From the MIR observations, we find that red-sequence galaxies consist not only of passively evolving red early-type galaxies, but also of (1) 'weak-SFGs' (disk-dominated star-forming galaxies that have star formation rates lower by similar to 4 x than blue-cloud galaxies) and (2) 'intermediate-MXGs' (bulge-dominated galaxies showing stronger MIR dust emission than normal red early-type galaxies). These two populations can be a set of transition galaxies from blue, star-forming, late-type galaxies evolving into red, quiescent, early-type ones. We find that the weak-SFGs are predominant at intermediate masses (10(10) M-circle dot < M-* < 10(10.5) M-circle dot) and are typically found in local densities similar to the outskirts of galaxy clusters. As much as 40% of the supercluster member galaxies in this mass range can be classified as weak-SFGs, but their proportion decreases to <10% at larger masses (M-* > 10(10.5) M-circle dot) at any galaxy density. The fraction of the intermediate-MXG among red-sequence galaxies at 10(10) M-circle dot < M-* < 10(11) M-circle dot also decreases as the density and mass increase. In particular, similar to 42% of the red-sequence galaxies with early-type morphologies are classified as intermediate-MXGs at intermediate densities. These results suggest that the star formation activity is strongly dependent on the stellar mass, but that the morphological transformation is mainly controlled by the environment.</P>