The local interstellar medium as traced by gamma rays
Caraveo, P. A.; Bignami, G. F.; Strong, A. W.; Hermsen, W.; Lebrun, F.; Buccheri, R.; Kanbach, G.; Mayer-Hasselwander, H. A.; Paul, J. A.; Wills, R. D.; Bloemen, J. B. G. M.
Italy, Netherlands, Germany, France
Abstract
Gamma-ray flux measurements (70-5000 MeV) made with the COS-B satellite have been used to study the distribution of total gas column density in the latitude range from 11 deg to 19 deg. A close correlation with the distribution found from galaxy counts exists. The dominant structure is associated with Gould's Belt, but several other major features are evident, possibly related to local structures inclined to the Galactic plane. A map of the distribution of molecular-hydrogen column density is presented based on the excess gamma-ray flux over that expected from atomic hydrogen. Taken together with a similar map derived from galaxy counts, the molecular-hydrogen angular distribution is established (on scales approximately 10 deg) with greater confidence than previously possible. The map derived from gamma-rays includes the southern celestial hemisphere for which galaxy-count coverage is not available.