EPoS Contribution
EPoS Contribution
What is the role of turbulence in molecular cloud formation and evolution?

Mordecai-Mark Mac Low
Dept of Astrophysics, American Museum of Natural History, New York, USA
Two countervailing views of the behavior of molecular clouds have become established over the past decade. On the one hand, the classical picture of molecular clouds as quasistatic objects supported by internal turbulence for many free-fall times has been updated to take into account our current understanding of the behavior of super-Alfvenic turbulence. In this picture, internal energy sources, particularly H II regions in the largest clouds, maintain microturbulent support of the cloud, so that the star formation rate per free-fall time remains no more than a few percent. On the other hand, increasing evidence has accumulated for a more dynamical picture, in which clouds form quickly in regions of compressive flow, whether from interstellar turbulence or large-scale gravitational instability, but then evolve equally quickly. In this picture, magnetic support of cloud envelopes contributes significantly to maintaining low global star formation rates, while cloud cores collapse quickly, without turbulent or magnetic support dominating. It has even been suggested that the initial formation of the clouds dominates their turbulent energy budget until they are torn apart by rapid star formation within. In this review I will attempt to surmount my own bias in favor of the latter view to give a critical evaluation of these two opposing views of cloud formation.

Suggested Session: Turbulence