THE EVOLUTION OF ACTIVE GALACTIC NUCLEI IN CLUSTERS OF GALAXIES TO REDSHIFT 1.3

Abstract

We have measured the luminous active galactic nucleus (AGN) population in a large sample of clusters of galaxies and find evidence for a substantial increase in the cluster AGN population from z ∼ 0.05 to z ∼ 1.3. The present sample now includes 32 clusters of galaxies, including 15 clusters above z = 0.4, which corresponds to a three-fold increase compared to our previous work at high redshift. At z< 0.4, we have obtained new observations of AGN candidates in six additional clusters and found no new luminous AGN in cluster members. Our total sample of 17 low-redshift clusters contains only two luminous AGNs, while at high redshifts there are 18 such AGNs, or an average of more than one per cluster. We have characterized the evolution of luminous X-ray AGNs as the fraction of galaxies with MR <M ∗ R (z) + 1 that host AGNs with rest-frame, hard X-ray [2–10 keV] luminosities LX,H 10 43 erg s −1 . The AGN fraction increases from fA = 0.134 +0.18 −0.087 % at a median z = 0.19 to fA = 1.00 +0.29 −0.23 %a t a median z = 0.72. Our best estimate of the evolution is a factor of 8 increase to z = 1 and the statistical significance of the increase is 3.8σ . This dramatic evolution is qualitatively similar to the evolution of the starforming galaxy population in clusters known as the Butcher–Oemler effect. We discuss the implications of this result for the coevolution of black holes and galaxies in clusters, the evolution of AGN feedback, searches for clusters with the Sunyaev–Zel’dovich effect, and the possible detection of environment-dependent downsizing.