Gamma rays from cosmic rays

A test of several aspects of the diffuse gamma-ray problem would involve the observation of gamma rays from known molecular clouds, taking into account the flux to be expected in connection with the interaction between ambient cosmic ray flux and the cloud. Preliminary estimates of the expected fluxes were made by Black and Fazio (1973). The present investigation is concerned with estimates on the basis of more recent interstellar medium (ISM) data and a comparison of the estimates with observations from both the SAS II and COS-B satellites. The obtained results give support to the idea that some, at least, of the so-called gamma-ray sources are molecular clouds irradiated by the ambient cosmic ray flux. Attention is also given to the fraction of the flux from both resolved and unresolved discrete sources and large-scale cosmic ray gradients. The gamma-ray evidence seems to point to a Galactic origin for low energy cosmic rays.