Summary: THE ASTROPHYSICAL JOURNAL, 546:980╚1005, 2001 January 10
( 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A.
DENSITY, VELOCITY, AND MAGNETIC FIELD STRUCTURE IN TURBULENT MOLECULAR
EVE C. OSTRIKER,1,2 JAMES M. STONE,1 AND CHARLES F. GAMMIE3
Received 2000 April 26; accepted 2000 September 1
We use three-dimensional (3D) numerical magnetohydrodynamic simulations to follow the evolution
of cold, turbulent, gaseous systems with parameters chosen to represent conditions in giant molecular
clouds (GMCs). We present results of three model cloud simulations in which the mean magnetic đeld
strength is varied kG for GMC parameters), but an identical initial turbulent velocity đeld(B
is introduced. We describe the energy evolution, showing that (1) turbulence decays rapidly, with the
turbulent energy reduced by a factor 2 after 0.4╚0.8 Đow crossing times (D2╚4 Myr for GMC parame-
ters), and (2) the magnetically supercritical cloud models gravitationally collapse after time B6 Myr,
while the magnetically subcritical cloud does not collapse. We compare density, velocity, and magnetic
đeld structure in three sets of model "" snapshots ¤¤ with matched values of the Mach number M B 9,7,5.
We show that the distributions of volume density and column density are both approximately log-
normal, with mean mass-weighted volume density a factor 3╚6 times the unperturbed value, but mean