The distribution of cosmic-ray electrons and nuclei in the Galaxy

Abstract

A detailed analysis is made of gamma-ray data from the SAS II and COS B satellite experiments and the data are taken, together with a variety of information on the density of gas in the ISM, to give the distribution of cosmic-ray flux in the Galaxy. Particular attention is given to problems caused by uncertainties in the column densities of molecular hydrogen. It is claimed that both the electron and the nuclear particle fluxes vary with position both over a region of a few kpc round the sun and over a larger region. For most of the Galaxy the variations are not large but if the most recent estimates of very considerable masses of molecular gas within 2 kpc of the Galactic centre are correct then the particle flux in this region is only some 10% of the local value. An analysis of the correlation of the gamma -ray flux with local gas in atomic and molecular forms (at latitudes in the range mod b mod =10 degrees -20 degrees ) has enabled the local gamma -ray emissivity spectrum to be determined. It is found that at the highest energies the emissivity with respect to molecular gas is lower than that with respect to atomic gas; possible reasons are discussed.