Cosmic rays, the metallicity gradient and the mass of molecular gas in the Galaxy

Abstract

Information on the metallicity gradient in the Galaxy is assessed and used to make a new estimate of the distribution of molecular hydrogen (H₂) in the Galaxy. it is found that the radial distribution of H₂ is rather different than thought hitherto and not too far from that of atomic hydrogen (H₁). Gamma-ray data above 35 MeV from the SAS II and COS B satellites have been used, together with the estimated masses of both H₂ and H₁, to determine the galactic distribution of cosmic rays under the assumption that the flux of gamma rays from unresolved sources is negligible. It is found that the intensity distribution (or electrons of several hundred MeV and protons of a few GeV) is similar to that of supernova remnants.