2013A&A...551A..20A

Cluster properties do not seem to be changing significantly during their mature evolution phase; for example, they do not seem to show any strong dynamical evolution at least up to z∼0.5, their galaxy red sequence is already in place at least up to z∼1.2, and their diffuse light content remains stable up to z∼0.8. The question is now to know if cluster properties can evolve more significantly at redshifts that are notably higher than 1. We propose here to see how the properties of the intracluster light (ICL) evolve with redshift by detecting and analysing the ICL in the X-ray cluster CL J1449+0856 at z=2.07, based on deep HST NICMOS H band exposures. We used the same wavelet-based method as one applied to 10 clusters between z=0.4 and 0.8. We detect three diffuse light sources with total magnitudes of H=24.8, 25.5, and 25.9, plus a more compact object with a magnitude H=25.3. We discuss the significance of our detections and show that they are robust. The three sources of diffuse light indicate an elongation along a north-east south-west axis, similar to that of the distribution of the central galaxies and to the X-ray elongation. This strongly suggests a history of merging events in this direction. While we found a roughly constant amount of diffuse light for clusters between z∼0 and 0.8, we prove at least a 1.5mag increase between z∼0.8 and 2. If we assume that the amount of diffuse light is directly linked to the infall activity on the cluster, this implies that CL J1449+0856 is still undergoing strong merging events.