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Summary: THE ASTROPHYSICAL JOURNAL, 546:980È1005, 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
CLOUD MODELS
EVE C. OSTRIKER,1,2 JAMES M. STONE,1 AND CHARLES F. GAMMIE3
Received 2000 April 26; accepted 2000 September 1
ABSTRACT
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 Ðeld
strength is varied kG for GMC parameters), but an identical initial turbulent velocity Ðeld(B
0
\ 1.4È14
is introduced. We describe the energy evolution, showing that (1) turbulence decays rapidly, with the
turbulent energy reduced by a factor 2 after 0.4È0.8 Ñow crossing times (D2È4 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
Ðeld structure in three sets of model "" snapshots ÏÏ 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 3È6 times the unperturbed value, but mean
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