THE CLUSTER AND FIELD GALAXY ACTIVE GALACTIC NUCLEUS FRACTION AT<i>z</i>= 1-1.5: EVIDENCE FOR A REVERSAL OF THE LOCAL ANTICORRELATION BETWEEN ENVIRONMENT AND AGN FRACTION

Abstract

The fraction of cluster galaxies that host luminous AGN is an important probe\nof AGN fueling processes, the cold ISM at the centers of galaxies, and how\ntightly black holes and galaxies co-evolve. We present a new measurement of the\nAGN fraction in a sample of 13 clusters of galaxies (M &gt;= 10^{14} Msun) at\n1&lt;z&lt;1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the\nfield fraction in the immediate vicinity of these clusters, and combine these\ndata with measurements from the literature to quantify the relative evolution\nof cluster and field AGN from the present to z~3. We estimate that the cluster\nAGN fraction at 1&lt;z&lt;1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,\nhard X-ray luminosity greater than L_{X,H} &gt;= 10^{44} erg/s. This fraction is\nmeasured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,\nwhere M*_{3.6}(z) is the absolute magnitude of the break in the galaxy\nluminosity function at the cluster redshift in the IRAC 3.6um bandpass. The\ncluster AGN fraction is 30 times greater than the 3sigma upper limit on the\nvalue for AGN of similar luminosity at z~0.25, as well as more than an order of\nmagnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} &gt;= 10^{43}\nerg/s exhibit similarly pronounced evolution with redshift. In contrast with\nthe local universe, where the luminous AGN fraction is higher in the field than\nin clusters, the X-ray and MIR-selected AGN fractions in the field and clusters\nare consistent at 1&lt;z&lt;1.5. This is evidence that the cluster AGN population has\nevolved more rapidly than the field population from z~1.5 to the present. This\nenvironment-dependent AGN evolution mimics the more rapid evolution of\nstar-forming galaxies in clusters relative to the field.\n