Extragalactic X-ray Astronomy

The identification and classification of extragalactic X-ray sources is discussed, with particular attention given to extended sources associated with clusters of galaxies and to compact sources found in the nuclei of active galaxies. Results obtained from the Uhuru spacecraft and the Ariel-V satellite provide most of the data for the identifications. Analysis of cluster X-ray spectra to yield information on the heating of gases and the nature of the intergalactic medium is discussed; investigation of the continuous X-ray spectra associated with active galaxies may clarify the problem of the energy source of active galaxies and quasars. Seyfert galaxies identified as X-ray sources and X-ray emitting components of the Perseus, Virgo, Centaurus and Coma clusters figure in the review.