The Mass-Size Relation from Clouds to Cores. II. Solar Neighborhood Clouds

Abstract

We measure the mass and size of cloud fragments in several molecular clouds continuously over a wide range of spatial scales ((0.05 <\sim r/pc <\sim 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) \alpha r^2), is not well suited to describe the derived mass-size data. Solar neighborhood clouds not forming massive stars ((< \sim 10 M \odot); Pipe Nebula, Taurus, Perseus, and Ophiuchus) obey (m(r) \leq 870 M \odot (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 \ \alpha \ r^{1.27}) (where the exponent is highly uncertain in any given cloud, but is certainly smaller than 1.5).