Intracluster light at z ∼ 0 . 25 from SDSS imaging data

We investigate the broadband optical emission of diffuse intergalactic stars in galaxy clusters at z ∼ 0.25 by means of an image stacking technique. The images of 654 clusters, selected with the max-BCG algorithm from a subsample of the SDSS-Data Release 1 (DR1), have been stacked after masking all the sources detected down to very low S/N. The resulting images in the g, r and i bands provide reliable photometric data at the level of & 30 mag/ ” (r band), out to & 600 kpc from the Brightest Cluster Galaxy (BCG). Our analysis shows that: i) the IntraCluster Light (ICL) is much more concentrated than the galaxy light, contributing ∼30% of the total cluster optical emission at R = 100 kpc, but less than 10% at R > 500 kpc; ii) the ICL contributes between 15 and 20% of the total cluster optical luminosity between the optical radius (μr = 25 mag/ ”) of the BCG and 500 kpc; iii) the colours of the ICL are consistent with the global colours of the cluster galaxies, with little evidence for redder g-r.