Intragroup and Intracluster Light
  The largest stellar halos in the universe are found in massive galaxy
clusters, where interactions and mergers of galaxies, along with the cluster
tidal field, all act to strip stars from their host galaxies and feed the
diffuse intracluster light (ICL) and extended halos of brightest cluster
galaxies (BCGs). Studies of the nearby Virgo Cluster reveal a variety of
accretion signatures imprinted in the morphology and stellar populations of its
ICL. While simulations suggest the ICL should grow with time, attempts to track
this evolution across clusters spanning a range of mass and redshift have
proved difficult due to a variety of observational and definitional issues.
Meanwhile, studies of nearby galaxy groups reveal the earliest stages of ICL
formation: the extremely diffuse tidal streams formed during interactions in
the group environment.
