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 ⊙ ). These findings were interpreted as an evidence ofvigorous, 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‐ μ 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‐ μ 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 clustercentric radii ∼200–500 kpc (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)