High-Latitude Molecular Clouds as Gamma-Ray Sources for the Gamma-Ray Large Area Space Telescope

Abstract

For about two decades, a population of relatively small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10° from the Galactic plane, these clouds have typical distances of ~150 pc, angular sizes of ~1°, and masses of order tens of solar masses. These objects are passive sources of high-energy γ-rays through cosmic-ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in γ-rays to have been detected by EGRET but that of order 100 of them will be detectable by the Large Area Telescope on the Gamma-Ray Large Area Space Telescope. Thus, we predict a new steady population of γ-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.