Constraints on a dense hot intergalactic medium

Abstract

A model is proposed in which exploding galaxies heat the intergalactic gas (IGG) to a temperature of 100 million to 1 billion K. The thermal bremsstrahlung from the model agrees with spectral measurements of the X-ray background (XRB). It is shown that recent submillimeter measurements of the cosmic microwave background (CMB) are consistent with a spectrum distorted from blackbody by Compton scattering on the same IGG. It is also shown that the isotropy and intensity of the XRB rule out its origin from discrete gas clouds. Because of the large energy requirement to heat the IGG and other considerations, the existence of a cosmologically significant amount of hot IGG must be regarded as uncertain. It is concluded that the amount of hot IGG corresponds to a critical density parameter of no more than 1.0.