Unresolved Galactic gamma ray sources and the determination of the CO/ conversion factor

Abstract

The derivation of the factor `X' used to convert the line integral of the emission over velocity to the column density of molecular hydrogen is a topic that has exercised the astronomical community for over a decade. Early work gave `high' values whereas we ourselves have consistently advocated a `low' value, specifically, for the Inner Galaxy, (see Bhat et al 1985 Nature 314 511, and later papers). Very recently, a new -ray value has come from the analysis of the EGRET data from the Compton Gamma Ray Observatory (CGRO) (Hunter et al 1996 Astrophys. J. in press). This new value is units but we here advocate its reduction by to allow for unresolved discrete sources.