THE PAN-STARRS1 MEDIUM-DEEP SURVEY: THE ROLE OF GALAXY GROUP ENVIRONMENT IN THE STAR FORMATION RATE VERSUS STELLAR MASS RELATION AND QUIESCENT FRACTION OUT TOz∼ 0.8

Abstract

Using a large optically-selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR) -stellar mass (M * ) relation, as well as the quiescent fraction versus M * relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10 14 M ⊙ ), we find a global reduction in the SSFR of the star forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass -the mass quenching plays a dominant role in producing quiescent galaxies for more massive galaxies, while less massive galaxies are quenched mostly through the environmental effect, with the transition mass around 1 − 2 × 10 10 M ⊙ in the group/cluster environment.

SPECTROSCOPIC STUDY OF STAR-FORMING GALAXIES IN FILAMENTS AND THE FIELD ATz∼ 0.5: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF ELECTRON DENSITY

“…-mass relations found here is consistent with several observational studies and large-scale hydrodynamical simulations, showing that, on average, many properties of starforming galaxies that are related to star-formation activity (such as color, SFR, sSFR, and SFR-mass relation) are independent of their host environment, a result that appears to hold regardless of the redshift, the method used to define environment, and the star-formation activity indicator (Peng et al 2010;Muzzin et al 2012;Wijesinghe et al 2012;Koyama et al 2013Koyama et al , 2014Darvish et al 2014;Hayashi et al 2014;Lin et al 2014;Vogelsberger et al 2014;Cen 2014). Hence, it has been argued that the major role of environment is to control the fraction of quiescent and star-forming systems (Peng et al 2010;Sobral et al 2011;Muzzin et al 2012;Darvish et al 2014;Vogelsberger et al 2014), that is, it is more likely for galaxies to become quenched in denser environments.…”

The Pan-STARRS1 Medium-deep Survey: Star Formation Quenching in Group and Cluster Environments

“…In our previous study, Lin et al (2014), we confirmed that the group environment strongly affects the fraction of quiescent galaxies at fixed stellar mass, but no environmental dependence was found for the star-forming sequence, in good agreement with previous works (Balogh et al 2004;Vulcani et al 2010;Koyama et al 2013). The result thus supports a fast environmentquenching scenario and favors galaxy mergers in groups as the primary quenching mechanism.…”

“…We hence extend our previous results to include the discussion of galaxy properties in terms of the projected group-centric radius r p and aim to understand at which radius the possible quenching mechanisms acting on galaxies effectively alter galaxy properties. This work is based on the same group catalog of two PS1 medium-deep fields, MD04 and MD07, produced by the probability friends-offriends (or PFOF) algorithm in Lin et al (2014). By taking advantage of the stacking technique plus background subtraction and removal of the field contamination, we obtain a finer correction for our stacked samples and thus more robust results than in our previous work.…”

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

“…From these same surveys it is possible to learn something about the evolving role of environment from measurements of local density or group catalogues (e.g. Giodini et al 2009;George et al 2011a;Knobel et al 2013;Lin et al 2014). In the context of the halo model (e.g.…”