The radial distribution of galactic gamma rays. II - The distribution of cosmic-ray electrons and nuclei in the outer galaxy

In the present derivation of the radial distribution of high energy gamma-ray emissivity in the outer Milky Way, the kinematics of H I are used to construct column-density maps in various galactocentric distance ranges that are then used in combination with COS-B spacecraft gamma-ray data to determine emissivities in these distance ranges. The results obtained imply a hardening of the gamma-ray spectrum with increasing distance, and include an energy-dependent decrease that is interpreted as a steep gradient in the cosmic-ray electron density and a near constancy of the nuclear component. The galactic origin of electrons with energies of up to several hundreds of MeVs is confirmed.