PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK

This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the (CO)-C-12 emission observed within b +/- 5 degrees. The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H-2 mass in the catalog is 1.2 x 10(9) M-circle dot, in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is R similar to 30 pc. We find that M proportional to R-2.2 +/- 0.2, with no correlation between the cloud surface density, Sigma, and R. In contrast with the general idea, we find a rather large range of values of Sigma, from 2 to 300 M-circle dot pc(-2), and a systematic decrease with increasing Galactic radius, R-gal. The cloud velocity dispersion and the normalization sigma(0) = sigma(v) R/(1/2) both decrease systematically with R-gal. When studied over the whole Galactic disk, there is a large dispersion in the line width-size relation and a significantly better correlation between sv and S R. The normalization of this correlation is constant to better than a factor of two for R-gal < 20 kpc. This relation is used to disentangle the ambiguity between near and far kinematic distances. We report a strong variation of the turbulent energy injection rate. In the outer Galaxy it may be maintained by accretion through the disk and/or onto the clouds, but neither source can drive the 100. times higher cloud-averaged injection rate in the inner Galaxy.