LoCuSS : a dynamical analysis of x-ray active galactic nuclei in local clusters.

We present a study of the distribution of X-ray active galactic nuclei (AGNs) in a representative sample of 26 massive clusters at 0.15 1042 erg s–1. In the stacked caustic diagram that shows (v los – v)/σ v versus r proj/r 500, the X-ray AGN appear to preferentially lie along the caustics, suggestive of an infalling population. They also appear to avoid the region with lowest cluster-centric radii and relative velocities (r proj 1042) and IR-bright (L TIR > 2 × 1010 L ☉) subsamples show higher velocity dispersions than their X-ray dim and IR-dim counterparts at >2σ significance. This is consistent with the nuclear activity responsible for the X-ray and IR emission being slowly shut down as the host galaxies are accreted into the cluster. Overall, our results provide the strongest observational evidence to date that X-ray AGNs found in massive clusters are an infalling population, and that the cluster environment very effectively suppresses radiatively efficient nuclear activity in its member galaxies. These results are consistent with the view that for galaxies to host an X-ray AGN they should be the central galaxy within their dark matter halo and have a ready supply of cold gas