X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution

TL;DR

This study analyzes X-ray point sources in 43 galaxy clusters, revealing an excess of AGN near cluster centers and a radial increase in AGN fraction, providing insights into galaxy activity in dense environments.

Contribution

It presents a catalog of X-ray sources in galaxy clusters and characterizes their spatial distribution, highlighting the radial dependence of AGN activity within clusters.

Findings

Approximately 1 excess X-ray source per cluster compared to blank fields.

Excess sources are concentrated within the virial radius, with a power-law radial profile.

The fraction of galaxies hosting AGN increases with distance from the cluster center.

Abstract

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 catalog of 4210 rigorously selected X-ray point sources in these fields, which span a survey area of 4.2 square degrees. This catalog reveals a clear excess of sources when compared to deep blank-field surveys, which amounts to roughly 1 additional source per cluster, likely Active Galactic Nuclei (AGN) associated with the clusters. The excess sources are concentrated within the virial radii of the clusters, with the largest excess observed near the cluster centers. The average radial profile of the excess X-ray sources of the cluster are well described by a power law (N(r) ~ r^\beta) with an index of \beta ~ -0.5. 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 5 to 10 times higher near the virial radius than in the central regions. This trend is qualitatively similar to that observed for star formation in cluster member galaxies.