Scattering of the Microwave Background in Clusters of Galaxies

Abstract

Evidence from X-ray observations of clusters of galaxies suggests that they contain intergalactic plasma at a temperature of approximately 108 K which emits thermal bremsstrahlung (cf. Lea et al. 1973). Although numerous models for the origin and distribution of the plasma have been presented (cf. Gould and Raphaeli 1978), the amount and distribution of the plasma is still not certain. Several years ago, Sunyaev and Zel-dovich (1972) pointed out another observable consequence of hot gas in clusters of galaxies: inverse Compton scattering by electrons in the plasma would increase the energy of photons of the microwave background as these photons pass through the cluster. The fractional change in intensity of the microwave background is: