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Cloud formation from large-scale instabilities

Published online by Cambridge University Press:  01 August 2006

Woong-Tae Kim
Woong-Tae Kim*
Affiliation:
Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-742, Republic of Korea email: [email protected]
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Abstract

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We discuss recent advances in cloud formation via gravitational instability under the action of self-gravity, magnetic fields, rotational shear, active stars, and/or stellar spiral arms. When shear is strong and the spiral arms are weak, applicable to flocculent galaxies at large, swing amplification exhibits nonlinear threshold behavior such that disks with a Toomre parameter Q < Qc experience gravitational runaway. For most realistic conditions, local models yield Qc ~ 1.4, similar to the observed star formation thresholds. When shear is weak, on the other hand, as in galactic central parts or inside spiral arms, magneto-Jeans instability is very powerful to form spiral-arm substructures including gaseous spurs and giant clouds. The wiggle and Parker instabilities proposed for cloud formation appear to be suppressed by strong non-steady motions inherent in vertically-extended spiral shocks, suggesting that gravitational instability is a primary candidate for cloud formation.

Keywords

galaxies: ISMinstabilitiesISM: kinematics and dynamicsISM: magnetic fieldsmethod: numericalMHDstars: formation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S237: Triggered Star Formation in a Turbulent ISM , August 2006 , pp. 351 - 357
Copyright
Copyright © International Astronomical Union 2007

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