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

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 3rd Law” of constant column density, m® = Cr^2, is not well suited to describe the derived mass-size data. Solar neighborhood clouds not forming massive stars (< 10 M_sun; Pipe Nebula, Taurus, Perseus, and Ophiuchus) obey m® < 870 M_sun (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 = Cr^1.27 (where the exponent is highly uncertain in any given cloud, but is certainly smaller than 1.5).