X-ray emission around radio galaxies in non-Abell clusters - A possible physical link between environment and nonthermal radio emission

Abstract

X-ray observations of a sample of 11 4C radio galaxies in clusters with z< or approx. =0.1 were performed with the IPC (resolution FWHMapprox.1'.5) on the Einstein Observatory. The sample galaxies lie in the directions of non-Abell Zwicky clusters; these clusters are generally poor, ranging in effective Abell richness class from < or approx. =0 to 1. In 10 out of the 11 observed fields 1--3 keV emission was detected. In nearly every case, the X-ray emission is centered on the radio galaxy; 5 out of 10 of the X-ray sources are resolved with HWHM of 70--300 kpc. The X-ray luminosities are (1--60) x 10/sup 42/ ergs s/sup -1/ (H/sub 0/ = 75 km s/sup -1/ Mpc/sup -1/), generally less than the richer Abell clusters and undetectable with previous satellites. Examinations of the optical fields and preliminary velocity data suggest that most of the radio sources are associated with dominant galaxies which are at rest at the gravitational centers of the clusters. Internal relativistic particle and magnetic field pressures of the relaxed outer radio structures are on the same order as the thermal pressure produced by the X-ray emitting gas. We argue that this class of radio source is confinedmore » (and possibly triggered) by gas accumulated at the cluster centers. The X-ray emission is a cosmic signpost indicating the presence of large quantities of gas around the central radio galaxies. Recent radio observations indicate that the probability of galaxy radio emission is much higher for cluster galaxies than for very isolated galaxies; these new X-ray observations of poor clusters combined with previous data on Abell clusters suggest that the presence of cluster gas is the important factor in determining the link between cluster environment and radio emission.« less