EXTRAGALACTIC X‐RAY SOURCES

Abstract

Surveys of the extragalactic X-ray sky based on data obtained from the Uhuru and Ariel V satellites are considered. The X-ray luminosity function of clusters is discussed the total density of X-ray clusters is found to approach that of all Abell clusters at a luminosity of 10 to the 43rd ergs/sec. It is concluded that for cluster X-ray sources, the bulk of the X-rays below about 10 keV result from thermal bremsstrahlung, predominantly from the cores of the clusters the mass of gas in the core is only a few percent of the total core binding mass, and the X-ray data are consistent with an iron abundance in the hot gas which is about half the cosmic value. Attention is also given to the structure of the nearby rich clusters Perseus, Virgo and Coma, to variability in Seyfert X-radiation and to high-excitation narrow emission line galaxies.