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Date and Time of the Query: 2019-06-26 T07:06:54 PDT
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For refcode 1991ApJ...367....1H:
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Copyright by American Astronomical Society. Reproduced by permission
1991ApJ...367....1H A CHANGE IN THE CLUSTER ENVIRONMENTS OF RADIO GALAXIES WITH COSMIC EPOCH G. J. HILL Institute for Astronomy, University of Hawaii; and University of Texas, McDonald Observatory AND S. J. LILLY Institute for Astronomy, University of Hawaii Received 1989 November 30; accepted 1990 June 25 ABSTRACT The results of an investigation into the cluster environments of radio galaxies spanning a wide range of radio power within a narrow range of redshift at z ~ 0.5 are presented. It is found that about half of the powerful classical double radio sources at z ~ 0.5 inhabit rich clusters, even though similar sources avoid such environments at low redshift. It is shown that this change includes not only the most powerful sources, but also sources of moderate power where a direct comparison with low-redshift sources is possible. The lowest power radio galaxies appear to inhabit similar environments at both epochs. In deriving these results, it is shown that the absolute magnitudes of the radio galaxies, and probably also of characteristic L^*^ galaxies, have not changed significantly since z ~ 0.5. The environments of the radio galaxies at z ~ 0.5 appear to be similar to those of quasars at similar redshifts studied by Yee and Green. The implications for our understanding of the cosmological evolution of the radio source population are discussed. Finally, it is suggested that an evolving intergalactic medium in rich clusters of galaxies could produce the observed change in cluster environment. Subject headings: cosmology - galaxies: clustering - quasars - radio sources: galaxies
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