X-ray bright active galactic nuclei in massive galaxy clusters - I. Number counts and spatial distribution

We present an analysis of the X-ray bright point-source population in 43 massive clusters of galaxies observed with the Chandra X-ray Observatory. We have constructed a catalogue of 4210 rigorously selected X-ray point sources in these fields, which span a survey area of 4.2 deg(2). This catalogue reveals a clear excess of sources when compared to deep blank-field surveys, which amounts to roughly 1 +/- 0.4 additional sources per cluster, likely active galactic nuclei (AGN) associated with the clusters. The excess sources are located within the overdensity radius r(500), with the largest excess observed near the cluster centres. The average radial profile of the excess X-ray sources of the cluster is well described by a power law [N(r) similar to r(beta)] with an index of beta similar to -0.6. An initial analysis using literature results on the mean profile of member galaxies in massive X-ray-selected clusters indicates that the fraction of galaxies hosting X-ray AGN rises with increasing clustercentric radius, being approximately three times higher near r(500) than in the central regions. This trend is qualitatively similar to that observed for star formation in cluster member galaxies.