CLASSICAL DOUBLE RADIO GALAXIES AND THEIR GASEOUS ENVIRONMENTS

A sample of classical double radio galaxies has been constructed to st udy the effect of environment on radio sources. The sample consists of radio galaxies in cluster and noncluster environments and includes ga laxies and clusters at both high (z similar to 0.5) and low (z similar to 0) redshift. Most of these radio galaxies are intermediate-power F R II sources with 408 MHz powers in the range from 10(32) to 10(35) h( -2) ergs s(-1) Hz(-1), where the upper bound corresponds roughly to a 178 MHz power of about 10(27) h(-2) W Hz(-1) sr(-1). Comparisons are m ade between the properties of FR II radio galaxies in cluster and nonc luster environments, and between X-ray clusters with and without FR II radio galaxies. The principal results are the following: 1. Most low- redshift FR II galaxies in clusters appear to be similar to FR II gala xies in group or held environments in terms of radio power, optical pr operties of the host galaxy, and nonthermal pressure of the radio brid ge. 2. High-redshift FR II galaxies are all quite similar and do not a ppear to vary with galactic environment. The radio powers and emission -line luminosities of the host galaxies of high-redshift FR II sources are higher on average than their low-redshift counterparts, but there is also overlap, and the nonthermal pressures of the radio bridges ap pear to be independent of redshift. 3. The nonthermal pressures of the bridges of FR II sources appear to be similar to the thermal pressure s of the ICM around them. This result, if confirmed by a larger sample , would allow the bridges of FR II sources to be used as probes of the ir gaseous environments. 4. The fact that most FR II galaxies have sim ilar nonthermal pressures, irrespective of galactic environment and re dshift, indicates that the gaseous environments around them are also s imilar. Typical nonthermal pressures of these FR II sources are much l ower than typical thermal pressures of the ICM in X-ray bright cluster s, suggesting that FR II sources are generally in environments with ga s pressures much less than typical low-redshift ICM pressures. 5. X-ra y data at low redshift show that clusters with FR II sources tend to b e underluminous in the X-ray compared to clusters without FR II source s. This suggests that the ICM pressures in these clusters are relative ly low, consistent with the results obtained from the analysis of the nonthermal pressures of FR II sources. 6. Unfortunately, the X-ray dat a for high-redshift clusters with FR II sources are inconclusive becau se of the large number of upper bounds involved and possible AGN contr ibution to the X-ray luminosity. However, the fact that most high-reds hift FR II radio galaxies have nonthermal pressures similar to their l ow-redshift counterparts indicates that the gaseous environments aroun d them are similar, in which case most high-redshift clusters with FR II sources should be underluminous X-ray emitters, as are their low-re dshift counterparts. 7. Thus, the evolution in the clustering strength around FR II sources toward high-redshift is likely to be closely lin ked to an evolution of the state of the intracluster medium. Namely, t here are more clusters of low gas pressure at high redshift, and thus more FR II sources can appear in these clusters. This is consistent wi th the negative evolution of the cluster X-ray luminosity function wit h redshift, and the fact that many high-redshift clusters have much lo wer X-ray luminosities than optically similar low-redshift clusters.