Small Molecular Clouds at High Latitudes as Gamma-Ray Sources for GLAST

Abstract

The sensitivity of the Large Area Telescope (LAT) on the forthcoming GLAST mission will be so much greater than previous high-energy {gamma}-ray missions that small molecular clouds at intermediate and high Galactic latitudes (|b| > 10{sup o}) will be detected in the light of diffuse {gamma}-ray emission from cosmic-ray interactions. These clouds are small, typically subtending less than 1{sup o} with masses {approx}10-100 solar and distances {approx}150 pc, and many are only now being discovered with sensitive, well-sampled, unbiased surveys of CO away from the Galactic equator. On the order of 100 such clouds will be detected by the LAT. Most will be near the detection limit (which depends on angular size) and many will in fact be detected but unresolved by the LAT, i.e., indistinguishable from point sources. We present predictions for the detectability of recently-cataloged clouds. As a {gamma}-ray source class, they will clearly have a Galactic distribution and be steady emitters, but identifications of these sources as molecular clouds rather than potentially more exotic {gamma}-ray phenomena will require more extensive and finely-sampled CO surveys at high latitudes.