Molecular Cloud Evolution IV. Magnetic Fields and Ambipolar Diffusion

Details Molecular Cloud Evolution IV. Magnetic Fields and Ambipolar Diffusion Molecular Cloud Evolution IV. Magnetic Fields and Ambipolar Diffusion

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21743436v&link_type=abstract

American Astronomical Society, AAS Meeting #217, #434.36; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

We investigate the formation and evolution of giant molecular clouds (GMCs) by the collision of convergent warm neutral medium (WNM) streams in the interstellar medium, in the presence of magnetic fields and ambipolar diffusion (AD), focusing on the evolution of the star formation rate (SFR) and efficiency (SFE), as well as of the mass-to-magnetic-flux ratio (M2FR) in the forming clouds. Our main results are: 1) A suite of simulations with global M2FRs 1.4, 0.9 and 0.7 spans a continuum of SFEs ranging from 35% to 3%. 2) The moderately subcritical run with M2FR=0.7 entirely shuts off its star formation activity after 4 Myr. 3) The fragmentation of the cloud by the combined action of thermal, gravitational, and nonlinear thin-shell instabilities produces dense clumps of high M2FR and low density patches of low M2FR. Thus, the M2FR is a highly fluctuating function of position, with the 3-sigma range spanning over one and a half dex in the M2FR. 4) We report the occurrence of an unexpected phenomenon of buoyancy of the low-M2FR regions within the gravitationally-contracting clouds.

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