The contribution of normal galaxies to the low energy gamma-ray cosmic diffuse background

Theories to explain the origin of the cosmic diffuse -ray background generally fall into one of two broad categories: those which attribute the emission to particle interctions in intergalactic space and those which attribute it to the summation of numerous, unresolved discrete sources, including normal field galaxies, active galactic nuclei and clusters of galaxies. Strong support for the latter interpretation is given by recent measurements of -ray emission from external galaxies, mainly Seyfert galaxies. Their summed contribution has been evaluated elsewhere; here instead, we use recent observational data on the -ray emission from our own galaxy to estimate the contribution of normal galaxies to the cosmic diffuse -radiation. Our result indicates that this contribution is limited to less than 0.1% and can therefore be neglected.