YZiCS: Preprocessing of dark halos in the hydrodynamic zoom-in
  simulation of clusters
  To understand the galaxy population in clusters today, we should also
consider the impact of previous environments prior to cluster infall, namely
preprocessing. We use YZiCS, a hydrodynamic high-resolution zoom-in simulation
of 15 clusters, and focus on the tidal stripping suffered by the dark matter
halos of cluster members due to preprocessing. We find ~48% of today's cluster
members were once satellites of other hosts. This is slightly higher than
previous estimates, in part, because we consider not just group-mass hosts, but
hosts of all masses also. Thus, we find the preprocessed fraction is poorly
correlated with cluster mass and is instead related to each cluster's recent
mass growth rate. Hosts less massive than groups are significant contributors,
providing more than one-third of the total preprocessed fraction. We find that
halo mass loss is a clear function of the time spent in hosts. However, two
factors can increase the mass loss rate considerably; the mass ratio of a
satellite to its host, and the cosmological epoch when the satellite was
hosted. The latter means we may have previously underestimated the role of high
redshift groups. From a sample of heavily tidally stripped members in clusters
today, nearly three quarters were previously in a host. Thus, visibly disturbed
cluster members are more likely to have experienced preprocessing. Being hosted
before cluster infall enables cluster members to experience tidal stripping for
extended durations compared to direct cluster infall and at earlier epochs when
hosts were more destructive.
