Gravity or Turbulence? The velocity dispersion-size relation

Abstract

We discuss the nature of the velocity dispersion vs. size relation for molecular clouds. In particular, we add to previous observational results showing that the velocity dispersions in molecular clouds and cores are not purely functions of spatial scale but involve surface gas densities as well. We emphasize that hydrodynamic turbulence is required to produce the first condensations in the progenitor medium. However, as the cloud is forming, it also becomes bound, and gravitational accelerations dominate the motions. Energy conservation in this case implies $|E_g|\sim E_k$, in agreement with observational data, and providing an interpretation for two recent observational results: the scatter in the $\delta v-R$ plane, and the dependence of the velocity dispersion on the surface density $\delta v^2/R\propto \Sigma$. We argue that the observational data are consistent with molecular clouds in a state of hierarchical gravitational collapse, i.e., developing local centers of collapse throughout the whole cloud while the cloud itself is collapsing, and making equilibrium unnecessary at all stages prior to the formation of actual stars. Finally, we discuss how this mechanism need not be in conflict with the observed star formation rate.

Accepted by MNRAS. 7 pages, 3 figures

References in corpus (9)

• Theory of Star Formation
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• Cooling, Gravity and Geometry: Flow-driven Massive Core Formation
• On the Structure of the Orion A Cloud and the Formation of the Orion Nebula Cluster
• Rapid Molecular Cloud and Star Formation: Mechanisms and Movies
• Six Myths on the Virial Theorem for Interstellar Clouds
• The Nature of the Velocity Field in Molecular Clouds. I. The Non-Magnetic Case

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