# A New Estimate of the Mass of Molecular Gas in the Galaxy and its Implications

C. L. Bhat, C. J. Mayer, A. W. Wolfendale

## Abstract

The amount of gas in the Galaxy and its distribution, both in space and between its various components, are among the 'constants' of the Galaxy. Clearly, this knowledge is a prerequisite for models of star formation, the chemical evolution of the interstellar medium and the manner of evolution of the Galaxy as a whole. The 21 cm hydrogen-line observations have led to a rather precise derivation of the distribution of atomic hydrogen (Hi), but the way in which the important, clumpy, molecular hydrogen (H$_{2}$) is distributed has been the subject of much discussion; it is this component that is the principal concern of the present work. We have examined a variety of data, including that from cosmic $\gamma$-rays, X-rays, infrared and millimetre-wave astronomy to compute the manner in which the surface density of H$_{2}$ varies with Galactocentric distance. The conclusion is that, in the inner Galaxy, the surface density is much less than previously thought. The total mass of H$_{2}$ in the inner Galaxy is estimated to be ca. [Note: Equation omitted. See the image of page 250 for this equation.], a value only some 60% of that in atomic hydrogen.