Molecular Clouds as Cosmic-Ray Barometers

The advent of high sensitivity, high resolution γ-ray detectors, together with a knowledge of the distribution of the atomic hydrogen and especially of the molecular hydrogen in the Galaxy on a subdegree scale, creates a unique opportunity to explore the flux of cosmic rays in the Galaxy. We here present the new data on the distribution of the molecular hydrogen from a large region of the inner Galaxy obtained by the NANTEN Collaboration. We then introduce a methodology which aims to provide a test bed for current and future γ-ray observatories to explore the cosmic-ray flux at various positions in our Galaxy. In particular, for a distribution of molecular clouds, as provided by the NANTEN survey, and local cosmic-ray density as measured at the Earth, we estimate the expected GeV to TeV γ-ray signal, which can then be compared with observations, and use to test the cosmic-ray flux.