2010ApJ...716..433K

We measure the mass and size of cloud fragments in several molecular clouds continuously over a wide range of spatial scales (0.05 ≲ r/pc ≲ 3). Based on the recently developed "dendrogram-technique," this characterizes dense cores as well as the enveloping clouds. "Larson's Third Law" of constant column density, m(r) {vprop} r ², is not well suited to describe the derived mass-size data. Solar neighborhood clouds not forming massive stars (≲10 M_☉; Pipe Nebula, Taurus, Perseus, and Ophiuchus) obey m(r) ≤ 870 M_☉(r/pc)^1.33. In contrast to this, clouds forming massive stars (Orion A, G10.15 - 0.34, G11.11 - 0.12) do exceed the aforementioned relation. Thus, this limiting mass-size relation may approximate a threshold for the formation of massive stars. Across all clouds, cluster-forming cloud fragments are found to be–at given radius–more massive than fragments devoid of clusters. The cluster-bearing fragments are found to roughly obey a mass-size law m {vprop} r ^1.27 (where the exponent is highly uncertain in any given cloud, but is certainly smaller than 1.5).