The Evolution of Active Galactic Nuclei in Clusters of Galaxies to
  Redshift 1.3
  We have measured the luminous 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 AGN, while at high redshifts
there are 18 such AGN, or an average of more than one per cluster. We have
characterized the evolution of luminous X-ray AGN as the fraction of galaxies
with M_R < M_R^*(z)+1 that host AGN with rest-frame, hard X-ray [2--10 keV]
luminosities L_X,H >= 10^43 \ergs. The AGN fraction increases from f_A =
0.134^{+0.18}_{-0.087} percent at a median z=0.19 to f_A = 1.00^{+0.29}_{-0.23}
percent at a median z=0.72. Our best estimate of the evolution is a factor of
eight increase to z=1 and the statistical significance of the increase is
3.8sigma. This dramatic evolution is qualitatively similar to the evolution of
the star-forming 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.
