X-Ray Emission from Clusters of Galaxies

We present a summary of X-ray spectral observations of ∼ 30 clusters of galaxies from HEAO-1. There exists strong correlations between X-ray luminosity, L x , and temperature kT in the form L x ∝ T 2.3 . This result combined with the L x vs. central galaxy density relation and the viral theorem indicates that the core radius of the gas should be roughly independent of L x or kT and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of kT with optical velocity dispersion, σ v , seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. We discuss the evidence for cooling in the cores of several clusters based on spectral observations with the Einstein Solid State Spectrometer.