Tidal stripping as a test of satellite quenching in redMaPPer clusters

Abstract

When dark matter haloes are accreted by massive host clusters, strong gravitational tidal forces begin stripping mass from the accreted subhaloes. This stripping eventually removes all mass beyond a subhalo's tidal radius, with unbound mass remaining in the vicinity of the satellite for at most a dynamical time t dyn . The N-body subhalo study of Chamberlain et al. verified this picture and pointed out a useful observational consequence: correlations between subhaloes beyond the tidal radius are sensitive to the infall time, t infall , of the subhalo on to its host. We perform this correlation using ∼160 000 red satellite galaxies in Sloan Digital Sky Survey redMaPPer clusters and find evidence that subhalo correlations do persist well beyond the tidal radius, suggesting that many of the observed satellites fell into their current host less than a dynamical time ago, t infall < t dyn . Combined with estimated dynamical times t dyn ∼ 3-5 Gyr and SED fitting results for the time at which satellites stopped forming stars, t quench ∼ 6 Gyr, we infer that for a significant fraction of the satellites, star formation quenched before those satellites entered their current hosts. The result holds for red satellites over a large range of cluster-centric distances 0.1-0.6 Mpc h −1 . We discuss the implications of this result for models of galaxy formation.

Kinematics of Cluster Galaxies and Their Relation to Galaxy Evolution

“…Our results suggest that, although this environmental effect of reducing the mass accretion on to halos can reproduce the spatial distribution of galaxies as a function of color, simultaneously explaining the velocity distribution may also require dependence of quenching on the nature of orbits of the galaxies within the cluster. It is also interesting to consider this result in light of previous results from SDSS RedMaPPer clusters suggesting that some red satellites entered their hosts recently, based on the persistence of satellite-satellite clustering within clusters (Fang et al 2016), while at least some blue satellites remain blue after a full crossing time within clusters, based on the presence of a splashback feature in their spatial distribution around clusters (Zürcher & More 2018). One possible explanation for the latter result, based on the kinematical measurements shown in Fig.…”

“…One possible explanation for this behavior is that a fraction of galaxies have entered their host clusters as members of subgroups, and were quenched before infall into their current hosts (Zabludoff & Mulchaey 1998;McGee et al 2009;Wetzel et al 2013). This should lead to an enhanced quiescent fraction in galaxies that are parts of subgroups within the cluster environment, a prediction that can be easily tested by repeating the analysis of Fang et al (2016) for blue satellites, and comparing to the previous result for red satellites.…”

“…Therefore, subhalo spatial correlations can be used as a clock, indicating the time since infall into their hosts. Fang et al (2016) measured this signal using satellites in RedMaPPer clusters. They found that a signicant fraction of the reddest galaxies have fallen in recently, arguing in favor of galaxies being quenched even prior to their infall into the host.…”

The galaxy–subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

“…Equation 16 assumes that faint cluster galaxies (which enter the source sample) do not cluster strongly with the bright cluster members constituting our lens sample; this small-scale cluster would introduce a dependence of B on θ ls . For reference, Fang et al (2016) showed that there is an excess of galaxies in the vicinity of cluster members, but at the level of a few galaxies per cluster, which would have no impact on our results. In fact, we find no evidence of small-scale clustering in our sample of red sequence galaxies.…”

Quenching of satellite galaxies at the outskirts of galaxy clusters

“…The 'starvation' quenching mode has been considered before (Larson et al 1980;Balogh et al 2000;McCarthy et al 2008;Bekki 2009;Vijayaraghavan & Ricker 2015) but usually under the assumption that the virial radius marked the edge of the system. As a result, the time-scales involved led to the conclusion that the process was not fast enough and that to match the observations of the quenched population, galaxies must have been quenched in the centres of smaller groups before becoming part of the cluster, a scenario known as 'pre-processing' (Balogh et al 2000;Jaffé et al 2012;Wetzel et al 2013;Fang et al 2016). However, if the edge of the ICM is much more extended and the gas reservoir in the haloes of individual galaxies is removed much earlier, one need not invoke 'pre-processed' or 'splashback' galaxies (Wetzel et al 2014) to account for the quenched population in clusters.…”