Dust-enshrouded star formation in XMM-LSS galaxy clusters

In recent years, infrared studies of individual galaxy clusters at intermediate redshifts led to the identification of several luminous infrared galaxies (L(IR) > 10(11) L(circle dot)). These findings were interpreted as an evidence of vigorous, dust-enshrouded star formation activity, hinting at the presence of an infrared Butcher-Oemler effect. In order to explore this effect, we have undertaken a statistical investigation based on a cluster sample drawn from the XMM-Newton Large Scale Structure survey (XMM-LSS) and exploiting the contiguous coverage of the XMM-LSS field by the Spitzer SWIRE legacy survey. We adopted a stacking technique to investigate the distribution of 24-mu m sources out to the cluster periphery and compare it with the distribution of sources in a sample of control fields. Among putative cluster members, selected by means of photometric redshifts, we identified surprisingly high numbers of bright 24-mu m sources toward intermediate redshift clusters (z > 0.3). Our analysis indicates the presence of an excess of bright mid-IR sources at redshift z > 0..3 at cluster-centric radii similar to 200-500 kpc. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim