THE GEMINI CLUSTER ASTROPHYSICS SPECTROSCOPIC SURVEY (GCLASS): THE ROLE OF ENVIRONMENT AND SELF-REGULATION IN GALAXY EVOLUTION ATz∼ 1

Abstract

We evaluate the effects of environment and stellar mass on galaxy properties at 0.85 < z < 1.20 using a 3.6µm-selected spectroscopic sample of 797 cluster and field galaxies drawn from the GCLASS survey. We confirm that for galaxies with LogM * /M ⊙ > 9.3 the well-known correlations between environment and properties such as star-forming fraction (f SF ), SFR, SSFR, D n (4000), and color are already in place at z ∼ 1. We separate the effects of environment and stellar mass on galaxies by comparing the properties of star-forming and quiescent galaxies at fixed environment, and fixed stellar mass. The SSFR of star-forming galaxies at fixed environment is correlated with stellar mass; however, at fixed stellar mass it is independent of environment. The same trend exists for the D n (4000) measures of both the star-forming and quiescent galaxies and shows that their properties are determined primarily by their stellar mass, not by their environment. Instead, it appears that environment's primary role is to control the fraction of star forming galaxies. Using the spectra we identify candidate poststarburst galaxies and find that those with 9.3 < LogM * /M ⊙ < 10.7 are 3.1 ± 1.1 times more common in high-density regions compared to low-density regions. The clear association of poststarbursts with high-density regions as well as the lack of a correlation between the SSFRs and D n (4000)s of starforming galaxies with their environment strongly suggests that at z ∼ 1 the environmental-quenching timescale must be rapid. Lastly, we construct a simple quenching model which demonstrates that the lack of a correlation between the D n (4000) of quiescent galaxies and their environment results naturally if self quenching dominates over environmental quenching at z > 1, or if the evolution of the self-quenching rate mirrors the evolution of the environmental-quenching rate at z > 1, regardless of which dominates.

Evidence for a change in the dominant satellite galaxy quenching mechanism atz = 1

“…3 we show, for the same samples, the fraction of all galaxies that are classified as passive, as a function of stellar mass. For the clusters, in the GCLASS sample, the fraction of passive galaxies is always much higher than it is in the z = 0.9 field from Ultravista (green, solid line), as previously shown by Muzzin et al (2012) and van der . This demonstrates that environment continues to play a significant role in determining galaxy properties at this redshift.…”

“…GCLASS (Muzzin et al 2012;van der Burg et al 2014) is a sample of 10 galaxy clusters at 0.85 < z < 1.35, selected from the 42 deg 2 SpARCS survey (Muzzin et al 2009;Wilson et al 2009;Demarco et al 2010). SpARCS makes use of deep z-band imaging in the SWIRE (Lonsdale et al 2003) fields to identify overdensities in z − [3.6] colour.…”

“…A related observation is that most star-forming galaxies in clusters have specific SFRs that are indistinguishable from those of field galaxies (e.g. Balogh et al 2004;Baldry et al 2006;Muzzin et al 2012;Mok et al 2013; Lin et al 2014). Wetzel et al (2013) suggest that these observations can be reconciled if the total quenching time is made up of a delay time t delay , during which there is little change to the SFR, and a final, much shorter 'fading time' t fade once the SFR begins to decrease.…”

“…Demarco et al 2007;Fassbender et al 2011;Muzzin et al 2012;Andreon et al 2014;Stanford et al 2014). Comparable work on more common, lower-mass haloes at z > 0.3 -the progenitors of today's massive clusters -is more difficult and hence more limited, but several studies have shown that group galaxies indeed evolve differently from the field, at least for z < 0.8 (e.g.…”

The structure and evolution of a forming galaxy cluster atz= 1.62

“…Distant clusters are the statistical ancestors of present-day clusters, so we can study the processes that drive galaxy evolution by comparing the galaxies within clusters at low and high redshifts. Distant clusters contain more blue, spiral galaxies with higher star formation rates than cluster members today (Poggianti et al 2009b), as well as a large fraction of post-starburst galaxies (Poggianti et al 2009a;Muzzin et al 2012) and a lack of low-mass red galaxies (e.g., De Lucia et al 2004;Rudnick et al 2012), all of which implies strong galaxy evolution.…”