1303.7231 (Andrew R. Wetzel et al.)

Galaxy evolution near groups and clusters: ejected satellites and the spatial extent of environmental quenching    [PDF]

Andrew R. Wetzel, Jeremy L. Tinker, Charlie Conroy, Frank C. van den Bosch

While satellite galaxies within groups/clusters are more likely to exhibit quiescent star formation rates (SFR) than central (field) galaxies, an enhanced quiescent likelihood extends to galaxies that are several virial radii beyond groups/clusters. Using a galaxy group/cluster catalog from SDSS DR7, we show that this enhancement has two causes. First, massive halos are clustered, so neighboring halos that host their own satellite galaxies boost the observed quiescent fraction out to large distances. Second, and more interestingly, central galaxies exhibit a strongly enhanced quiescent fraction out to 2.5 virial radii (with some enhancement out to 5 virial radii) beyond groups/clusters. We show that this enhancement for central galaxies can be explained by 'ejected' satellite galaxies that orbit beyond their host halo's virial radius. Using a cosmological N-body simulation, we examine the orbital histories of ejected satellites, showing that they extend out to 2.5 virial radii beyond their host halo and compose up to 40% of all central galaxies out to this distance. After ejection, these satellites typically orbit for several Gyr beyond the virial radius before falling back in, during which time they (continue to) lose significant halo mass. We show that a model in which ejected satellites experience the same SFR evolution and quenching as satellites within a host halo can explain essentially all environmental dependence of galaxy quenching beyond a host halo's virial radius. The strong halo mass stripping of ejected satellites also reduces the average halo masses of galaxies near massive groups/clusters, an effect that is potentially observable via weak lensing. Overall, the SFRs/colors and stellar/halo masses of ejected satellites present challenges for the standard halo model for galaxy occupation and highlight the importance of environmental history in galaxy evolution.

View original: http://arxiv.org/abs/1303.7231