FORMATION OF MAGNETIZED PRESTELLAR CORES WITH AMBIPOLAR DIFFUSION AND TURBULENCE

We investigate the roles of magnetic fields and ambipolar diffusion during prestellar core formation in turbulent giant molecular clouds, using three-dimensional numerical simulations. Our simulations focus on the shocked layer produced by a converging large-scale flow and survey varying ionization...

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Bibliographic Details
Published in:The Astrophysical journal 2014-04, Vol.785 (1), p.1-20
Main Authors: Chen, Che-Yu, Ostriker, Eve C
Format: Article
Language:English
Subjects:
AMBIPOLAR DIFFUSION
ANISOTROPY
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Computational fluid dynamics
Computer simulation
COMPUTERIZED SIMULATION
HYDRODYNAMIC MODEL
IONIZATION
LAYERS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MASS
Mathematical models
SOUND WAVES
STAR ACCRETION
STARS
THREE-DIMENSIONAL CALCULATIONS
TRANSIENTS
TURBULENCE
Turbulent flow
VELOCITY
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Summary:We investigate the roles of magnetic fields and ambipolar diffusion during prestellar core formation in turbulent giant molecular clouds, using three-dimensional numerical simulations. Our simulations focus on the shocked layer produced by a converging large-scale flow and survey varying ionization and the angle between the upstream flow and magnetic field. We also include ideal magnetohydrodynamic (MHD) and hydrodynamic models. From our simulations, we identify hundreds of self-gravitating cores that form within 1 Myr, with masses M ~ 0.04-2.5 M sub([middot in circle]) and sizes L ~ 0.015-0.07 pc, consistent with observations of the peak of the core mass function. Median values are M = 0.47 M sub([middot in circle]) and L = 0.03 pc. Core masses and sizes do not depend on either the ionization or upstream magnetic field direction. In contrast, the mass-to-flux ratio does increase with lower ionization, from twice to four times the critical value. The higher mass-to-flux ratio for low ionization is the result of enhanced transient ambipolar diffusion when the shocked layer first forms. However, ambipolar diffusion is not necessary to form low-mass supercritical cores. For ideal MHD, we find similar masses to other cases. These masses are one to two orders of magnitude lower than the value M sub(mag,sph) = 0.007B super(3)/(G super(3/2)[rho] super(2)) that defines a magnetically supercritical sphere under post-shock ambient conditions. This discrepancy is the result of anisotropic contraction along field lines, which is clearly evident in both ideal MHD and diffusive simulations. We interpret our numerical findings using a simple scaling argument that suggests that gravitationally critical core masses will depend on the sound speed and mean turbulent pressure in a cloud, regardless of magnetic effects.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/785/1/69