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 hundreds 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 the total cluster light at z similar to 1 using deep J-band (1.2 mu m) imaging from a high-acuity wide-field K-band imager on the Very Large Telescope. We investigate the ICL in six X-ray selected galaxy clusters at 0.8 = z similar to 1.2 and find that the ICL below isophotes mu J = 22 mag?arcsec-2 constitutes 14 per cent 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 of 24 since z similar to 1. We also find the fraction of the total cluster light contained within the brightest cluster galaxy (BCG) to be 2.06.3 per cent at these redshifts, which in five out of six cases is larger than the fraction of the ICL component, in contrast to the 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 amount 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 and the observed large masses and scale sizes reported for BCGs at high redshift.