Gamma-ray emission from atomic and molecular gas at intermediate galactic latitudes

Abstract

Recent developments in the study of the correlations between gamma-rays and local gas tracers are described. COS-B data in the range between b of 10 and 20 deg are analyzed using simultaneous 21-cm and galaxy count data, in order to separate the roles of atomic and molecular gas. The new galaxy-count calibration of Strong (1983) is used, and the results compared with those for the calibration of Strong and Lebrun (1982). The contribution from inverse Compton scattering is modelled, and its absolute intensity, derived by fitting to the data, is in accord with that expected from known interstellar radiation fields. The resulting total predicted intensities from atomic and molecular gas and inverse Compton scattering are in better accord with the data than in earlier work (Strong et al., 1982), which used only galaxy-counts and which ignored possible differences between the emission associated with the two gas phases as well as the Compton component. The results in the three energy ranges considered indicate a flatter spectrum for the gas emissivity than previously found, at least for the component correlated with the H I. If it is assumed that the atomic and molecular correlated components have the same spectral shape, the absolute emissivities do not differ by more than 30 percent.