On the Origin of Intracluster Light in Massive Galaxy Clusters
  We present a pilot study on the origin and assembly history of the ICL for
four galaxy clusters at 0.44<z<0.57 observed with the Hubble Space Telescope
from the Cluster Lensing and Supernova Survey with Hubble (CLASH) sample. Using
this sample of clusters we set an empirical limit on the amount of scatter in
ICL surface brightness profiles of such clusters at z=0.5 and constrain the
progenitor population and formation mechanism of the ICL by measuring the ICL
surface brightness profile, the ICL color and color gradient, and the total ICL
luminosity within 10<r<110 kpc. The observed scatter is physical, which we
associate with differences in ICL assembly process, formation epoch, and/or ICL
content. Using stellar population synthesis models we transform the observed
colors to metallicity. For three of the four clusters we find clear negative
gradients that, on average, decrease from super solar in the central regions of
the BCG to sub-solar in the ICL. Such negative color/metallicity gradients can
arise from tidal stripping of L* galaxies and/or the disruption of dwarf
galaxies, but not major mergers with the BCG. We also find that the ICL at 110
kpc has a color comparable to m*+2 red sequence galaxies and a total luminosity
between 10<r<110 kpc of 4-8 L*. This suggests that the ICL is dominated by
stars liberated from galaxies with L>0.2 L* and that neither dwarf disruption
nor major mergers with the BCG alone can explain the observed level of
luminosity and remain consistent with either the observed evolution in the
faint end slope of the luminosity function or predictions for the number of BCG
major mergers since z=1. Taken together, the results of this pilot study are
suggestive of a formation history for these clusters in which the ICL is
built-up by the stripping of >0.2 L* galaxies, and disfavor significant
contribution to the ICL by dwarf disruption or major mergers with the BCG.
