Mordecai-Mark Mac Low
Published 2002-01-10, updated 2002-09-23Version 2
MHD turbulence plays a central role in the physics of star-forming molecular clouds and the interstellar medium. I here show that MHD turbulence in molecular clouds must be driven to account for the observed supersonic motions in the clouds, as even strongly magnetized turbulence decays quickly. I then show that driven MHD turbulence can globally support gravitationally unstable regions, but local collapse inevitably occurs. Differences in the strength of driving and the gas density may explain the very different rates of star formation observed in different galaxies. The driving mechanism for the turbulence is likely a combination of field supernovae in star-forming sections of galactic disks, and magnetorotational instabilities in outer disks and low surface brightness galaxies. Supernova-driven turbulence has a broad range of pressures with a roughly log-normal distribution. High-pressure, cold regions can be formed even in the absence of self-gravity.
Comments: 30 pages, 18 figures (last four color on pages 24 and after); final refereed version to be published in the conference proceedings "Simulations of magnetohydrodynamic turbulence in astrophysics" eds. T. Passot & E. Falgarone, Springer Lecture Notes in Physics (changes in response to referee's comments were primarily for clarity, in some cases making drastic improvements.)
Journal: Lect.Notes Phys. 614 (2003) 182-212
Star formation and the interstellar medium in low surface brightness galaxies. III. Why they are blue, thin and poor in molecular gas
Modelling the Interstellar Medium of Low Surface Brightness Galaxies: Constraining Internal Extinction, Disk Color Gradients, and Intrinsic Rotation Curve Shapes
Glimpses of the Interstellar Medium at Redshift 3.5
