Measurement of the intracluster light at z ~ 1
  A significant fraction of the total photospheric light in nearby galaxy
clusters is thought to be contained within the diffuse intracluster light
(ICL), which extends 100s of kpc from cluster cores. The study of the ICL can
reveal details of the evolutionary histories and processes occurring within
galaxy clusters, however since it has a very low surface brightness it is often
difficult to detect. We present here the first measurements of the ICL as a
fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m)
imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected
galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) =
22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius
R500. This is broadly consistent with simulations of the ICL at a similar
redshift and when compared to nearby observations suggests that the fraction of
the total cluster light that is in the ICL has increased by a factor 2 - 4
since z\sim1. We also find the fraction of the total cluster light contained
within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts,
which in 5 out of 6 cases is larger than the fraction of the ICL component, in
contrast to results from nearby clusters. This suggests that the evolution in
cluster cores involves substantial stripping activity at late times, in
addition to the early build up of the BCG stellar mass through merging. The
presence of significant amounts of stellar light at large radii from these BCGs
may help towards solving the recent disagreement between the semi-analytic
model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the
observed large masses and scale sizes reported for BCGs at high redshift.
