High-Latitude Molecular Clouds as gamma-ray Sources for GLAST

Abstract

For about two decades, a population of relative small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10$^\circ$ from the Galactic plane, these clouds have typical distances of $\sim$150 pc, angular sizes of $\sim1^\circ$, 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 (LAT) on GLAST. Thus, we predict a new steady population of $γ$-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.