Intracluster light in clusters of galaxies at redshifts 0.4 <z< 0.8

Abstract

Context. The study of intracluster light (ICL) can help us to understand the mechanisms taking place in galaxy clusters, and to place constraints on the cluster formation history and physical properties. However, owing to the intrinsic faintness of ICL emission, most searches and detailed studies of ICL have been limited to redshifts z < 0.4. Aims. To help us extend our knowledge of ICL properties to higher redshifts and study the evolution of ICL with redshift, we search for ICL in a subsample of ten clusters detected by the ESO Distant Cluster Survey (EDisCS), at redshifts 0.4 < z < 0.8, that are also part of our DAFT/FADA Survey. Methods. We analyze the ICL by applying the OV WAV package, a wavelet-based technique, to deep HST ACS images in the F814W filter and to V-band VLT/FORS2 images of three clusters. Detection levels are assessed as a function of the diffuse light source surface brightness using simulations. Results. In the F814W filter images, we detect diffuse light sources in all the clusters, with typical sizes of a few tens of kpc (assuming that they are at the cluster redshifts). The ICL detected by stacking the ten F814W images shows an 8σ detection in the source center extending over a ∼50 × 50 kpc 2 area, with a total absolute magnitude of −21.6 in the F814W filter, equivalent to about two L * galaxies per cluster. We find a weak correlation between the total F814W absolute magnitude of the ICL and the cluster velocity dispersion and mass. There is no apparent correlation between the cluster mass-to-light ratio (M/L) and the amount of ICL, and no evidence of any preferential orientation in the ICL source distribution. We find no strong variation in the amount of ICL between z = 0 and z = 0.8. In addition, we find wavelet-detected compact objects (WDCOs) in the three clusters for which data in two bands are available; these objects are probably very faint compact galaxies that in some cases are members of the respective clusters and comparable to the faint dwarf galaxies of the Local Group. Conclusions. We show that the ICL is prevalent in clusters at least up to redshift z = 0.8. In the future, we propose to detect the ICL at even higher redshifts, to determine wether there is a particular stage of cluster evolution where it was stripped from galaxies and spread into the intracluster medium.

The XXL Survey

“…To detect the diffuse light, we applied the same tool as in Adami et al (2013) and Guennou et al (2012). This is a wavelet-based method (the OV_WAV package, see e.g.…”

“…We considered characteristic scales between 1 and 512 pixels in wavelet space (the 1024 pixel scale as in Guennou et al 2012 did not provide any additional detection). The object image was then subtracted from the sky image to produce the residual image.…”

“…This residual image includes both hidden features that are typically too faint to satisfy the wavelet first-pass thresholding conditions and the diffuse light patches, which are too faint to be detected as objects. We did not have to use a second iteration of this process as in Guennou et al (2012) as the data were of sufficient quality to detect all objects of interest in the first pass.…”

“…Coma, Centaurus, Virgo, Perseus, Norma) and the total amount of ICL is almost always equivalent at maximum to a few L galaxies in massive clusters (e.g. Guennou et al 2012). From a general point of view, the ICL contribution to the cluster luminosity is less than a few dozen percentage points.…”

“…The existence of such a system is puzzling in the common scenarios of ICL formation (e.g. Guennou et al 2012). While ICL is expected to be efficiently formed in clusters/groups, the amount observed in XLSSC 116 is exceptional and likely indicates recent strong dynamical interactions within the cluster.…”