The Evolution of Cluster Radio Galaxies from [CLC][ITAL]z[/ITAL][/CLC] = 0 to [CLC][ITAL]z[/ITAL][/CLC] = 0.8

Abstract

A radio continuum survey of a complete sample of distant (z = 0.3?0.8) X-ray?selected clusters has been conducted at 20 cm with the Very Large Array (VLA). The targets for this survey are the complete sample of 19 distant clusters found in the X-ray?selected Einstein Extended Medium Sensitivity Survey (EMSS) at z ? 0.3 and ? ? -20?. This survey is complete to a limiting point-source radio power level of log P ? 23.5 W Hz-1 (H0 = 75 km s-1 Mpc-1 and q0 = 0.1) out to ? Abell cluster radius from the brightest cluster galaxy close to the X-ray emission centroid. Of the total of 41 radio sources detected within ? Abell radius, 23 are associated with galaxies in these clusters. Higher angular resolution mapping of these cluster radio galaxies provides details of their structure and morphology. A comparison of the radio power levels, radio structure, position in the cluster, and the total number of these radio galaxies finds no evidence for any significant differences compared to nearby rich cluster radio galaxies. The radio luminosity function of distant cluster radio galaxies is statistically indistinguishable from that seen nearby. Taken together with the minimal evolution seen in the number of rich clusters over the same time period, this provides substantial evidence for no evolution in the population of rich cluster radio galaxies since z ~ ?. The results of this radio continuum survey differ from those studies that took the opposite approach, in which a radio-loud quasar or FR 2 radio galaxy was used as a target for a rich cluster search. While those studies found numerous FR 2's and quasars in rich clusters at z ~ ?, this survey has found only FR 1?type sources. The difference between these two approaches may lie in the density of the intracluster medium (ICM) and the galaxy richness of the clusters in these two samples, with the current sample having the demonstrably denser ICMs and richer galaxy populations.