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

TL;DR

This study measures the mass and size of molecular cloud fragments across various scales in the solar neighborhood, revealing different mass-size relations for clouds forming massive stars and those that do not, and identifying potential thresholds for massive star formation.

Contribution

It introduces a dendrogram-based method to characterize cloud fragments over a wide range of scales and compares mass-size relations across different cloud types and star formation activities.

Findings

Clouds not forming massive stars follow m(r) < 870 M_sun (r/pc)^1.33.

Clouds forming massive stars exceed the above relation.

Cluster-forming fragments are more massive at given radii and follow m = C*r^1.27.

Abstract

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).