OSO 8 X-ray spectra of clusters of galaxies. II - Discussion

Abstract

The Goddard Space Flight Center 2--20 keV OSO 8 data on X-ray clusters are examined for information which will restrict models for hot intracluster gas structures. From the correlation between X-ray temperature and velocity dispersion, we conclude that the X-ray core radius should be less than the galaxy core radius. Thus fits of X-ray profiles of clusters to isothermal spheres yield a core radius approximately equal to the density cutoff radius rather than the true core radius. If we instead assume a generalized polytropic structure, from the same correlation we may conclude that the gas is more nearly isothermal than adiabatic within a few core radii of the center. Therefore we require thermal conduction, radiative cooling, or both in cluster atmospheres. In both of these interpretations, the Coma cluster and possibly Abell 2319 A are quite discrepant.From the correlation between bremsstrahlung emission integral and temperature, we conclude that hotter clusters contain a larger fraction of their virial mass in the form of gas emitting in the 2--20 keV band. We find that the '/sup 7/central concentration factor'' for the emission cannot vary with temperature steeply enough to account for the correlation.We closely examine relations among the various measures of galaxymore » density and optical cluster morphology. There is evidence for real correlations between optical central cluster properties and X-ray properties which are not ''artifacts'' of underlying richness correlations as suggested by Jones and Forman.We also predict a population of cool, dim X-ray cluster which has not been observed.From consideration of the errors in published atomic physics data and spectrum calculations, we conclude that the iron abundance determinations recently quoted for intracluster gas are uncertain by from 50% to greater than 100% from this nonstatistical cause alone.« less