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(r) = C*r^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(r) < 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 =
C*r^1.27 (where the exponent is highly uncertain in any given cloud, but is
certainly smaller than 1.5).
