Spectra of radio galaxies in clusters

The discovery of powerful X-ray emission with an apparently thermal spectrum from a considerable number of clusters has been attributed to a hot intracluster gas. Such a gas surrounding a radio galaxy may conceivably retard the expansion or diffusion of the relativistic electrons. This would eventually result in a steepening of the radio spectrum caused by synchrotron radiation losses. Surveys of clusters identified with powerful X-ray emitters have indeed shown that the spectra of radio sources near the centers of such clusters are much steeper than those of field galaxies. The present investigation extends such spectral observations to a large sample of Abell clusters, most of which are not powerful X-ray emitters. The obtained results support the hypothesis that the spectra of radio galaxies near the centers of clusters will be steepened by the confining influence of a hot, relatively dense electron gas.