Gamma ray emission from a baryonic dark halo+

Abstract

A re-analysis of EGRET data by Dixon et al has led to the discovery of a statisticallysignificant diffuse γ-ray emission from the galactic halo. We show that this emission can naturally be accounted for within a previously proposed model for baryonic dark matter, according to which dark clustersof brown dwarfs and cold self-gravitating H2 clouds populate the outer galactic halo and can show up in microlensing observations.Basically, cosmic-ray protons in the galactic halo scatter on the clouds clumped into dark clusters, giving rise to the observed γ-ray flux. We derive maps for the corresponding intensity distribution, which turnout to be in remarkably good agreement with those obtained byDixon et al. We also address future prospects to test our predictions.