γ Rays from the cosmic ray irradiation of local molecular clouds

An analysis is given here of the flux of cosmic γ rays of energy above 100 MeV from the directions of 13 local molecular clouds. We show that only in a few clouds does the cosmic ray intensity need to exceed the value near the Earth to explain the γ-ray fluxes. Possible reasons for the few excesses are considered. Our conclusion is important because some of the enigmatic γ-ray `sources' are identified; furthermore, γ-ray data can be coupled with knowledge about the distribution of gas in the Galaxy to throw light on the problem `where do cosmic rays come from?'.