X-rays from Hot Plasma in Clusters of Galaxies.Commentary

To disentangle the X-ray emissions from clusters of galaxies, we study the simple limiting model of Bremsstrahlung emission by a static hot plasma in the potential well set up by a cluster. The gas distribution is related simply and exactly to the galaxy counts, given the "equation of state". We find a good fit to the existing data on the X-ray luminosity distribution, with no free parameters, for an isothermal gas conforming to the King distribution of galaxies, which is suggested by optical evidence for the best studied case of Coma cluster. An adiabatic gas fits less closely the extended emissions found from UHURU data. As the evidence for the latter is not yet fully established, we discuss implications of the models, and other discriminating observations.