Physical properties of molecular clouds for the entire Milky Way disk.
MIVILLE-DESCHENES M.-A., MURRAY N. and LEE E.J.
Abstract (from CDS):
This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the 12CO emission observed within b±5°. 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 H2 mass in the catalog is 1.2×109 M☉, 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∼30 pc. We find that M∝ R^2.2±0.2^, with no correlation between the cloud surface density, Σ, and R. In contrast with the general idea, we find a rather large range of values of Σ, from 2 to 300 M☉ pc–2, and a systematic decrease with increasing Galactic radius, Rgal. The cloud velocity dispersion and the normalization σ0=σv/R1/2 both decrease systematically with Rgal. When studied over the whole Galactic disk, there is a large dispersion in the line width-size relation and a significantly better correlation between σv and Σ R. The normalization of this correlation is constant to better than a factor of two for Rgal 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.