Environmental Dependences of IR-Bright AGN Incidence in Massive Galaxy Clusters

The number of active galactic nuclei (AGN) in galaxy clusters has been observed to grow by nearly two orders of magnitude from the local universe to z ~ 1.5. Star formation rates in clusters have also been observed to rise rapidly over this redshift interval. These trends, along with several other recent observations of high-redshift clusters, have led to the idea that this enhanced star formation and AGN activity may be driven by galaxy mergers within the clusters. Since mergers are more efficient in lower mass clusters with smaller galaxy velocity dispersions, the expectation is that AGN incidence should scale inversely with cluster mass. Studies using X-ray selected AGN has offered some support for this model in low-redshift clusters, though with large uncertainties. We select infrared bright AGN from a large, uniform, mass-selected galaxy cluster sample from the South Pole Telescope spanning a redshift range of 0.15 = z = 1.7. With these data we explore the incidence of IR-bright AGN in clusters as a function of cluster mass, redshift, and projected cluster-centric radius. We find evidence of an inverse mass relation between the halo mass and the incidence rate of IR-bright AGN along the lines of sight to massive galaxy clusters which further corroborates a merger-driven AGN triggering mechanism in massive galaxy clusters.