Backsplash galaxies in isolated clusters
  At modest radii from the centre of galaxy clusters, individual galaxies may
be infalling to the cluster for the first time, or have already visited the
cluster core and are coming back out again. This latter population of galaxies
is known as the backsplash population. Differentiating them from the infalling
population presents an interesting challenge for observational studies of
galaxy evolution. To attempt to do this, we assemble a sample of 14 redshift-
and spatially-isolated galaxy clusters from the Sloan Digital Sky Survey. We
clean this sample of cluster-cluster mergers to ensure that the galaxies
contained within them are (to an approximation) only backsplashing from the
centre of their parent clusters and are not being processed in sub-clumps. By
stacking them together to form a composite cluster, we find evidence for both
categories of galaxies at intermediate radii from the cluster centre.
Application of mixture modelling to this sample then serves to differentiate
the infalling galaxies (which we model on galaxies from the cluster outskirts)
from the backsplash ones (which we model on galaxies in the high density core
with low velocity offsets from the cluster mean). We find that the fraction of
galaxies with populations similar to the low velocity cluster core galaxies is
f = -0.052R/R_virial + 0.612 +/- 0.06 which we interpret as being the
backsplash population fraction at 1<R/R_virial<2. Although some interlopers may
be affecting our results, the results are demonstrated to be in concordance
with earlier studies in this area that support density-related mechanisms as
being the prime factor in determining the star formation rate of a galaxy.
