Galaxy evolution near groups and clusters: ejected satellites and the
  spatial extent of environmental quenching
  Galaxies that are several virial radii beyond groups/clusters show
preferentially quiescent star formation rates. Using a galaxy group/cluster
catalog from the Sloan Digital Sky Survey, together with a cosmological N-body
simulation, we examine the origin of this environmental quenching beyond the
virial radius. Accounting for the clustering of groups/clusters, we show that
central galaxies show enhanced SFR quenching out to 2.5 virial radii beyond
groups/clusters, and we demonstrate that this extended environmental
enhancement can be explained simply by 'ejected' satellite galaxies that orbit
beyond their host halo's virial radius. We show that ejected satellites
typically orbit for several Gyr beyond the virial radius before falling back
in, and thus they compose up to 40% of all central galaxies near
groups/clusters. We show that a model in which ejected satellites experience
the same SFR quenching as satellites within a host halo can explain essentially
all environmental dependence of galaxy quenching. Furthermore, ejected
satellites (continue to) lose significant halo mass, an effect that is
potentially observable via gravitational lensing. The SFRs/colors and
stellar-to-halo masses of ejected satellites highlight the importance of
environmental history and present challenges to models of galaxy occupation
that ignore such history.
