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R. Shetty, E. C. Ostriker (University of Maryland)
We investigate the formation of substructure in spiral galaxies using global MHD simulations, including self gravity. Local modeling by Kim and Ostriker (2002) has shown that self gravity and magnetic fields cause the growth of high density clumps in the spiral arms rather rapidly; subsequently, these clumps result in the formation of sheared, feather like structures in the interarms, known as spurs. Global modeling extends the study of local models by including the effects of the global spiral perturbation, total self gravitational contribution, as well as the density variation with radius. We show that self gravity, in combination with galactic differential rotation, can cause the growth of filamentary structures in disk galaxies, regardless of the strength, or even presence, of the external spiral potential. However, a sufficiently strong sprial potential is required to produce spurs, which are the filamentary structures distinctly associated with the spiral arms, having near-perpendicular intersections with the main dust lane. The properties of spurs, such as formation timescales, shapes, and spacing, depend mainly on the Toomre instability parameter and the relative velocity of the gas and the pattern speed of the background spiral potential. Based on these properties, it is possible to distinguish spur structures that originate as instabilities in the arms, from "background" filaments that become organized by a growing spiral pattern.
This research is supported by the National Science Foundation under grant AST-0507315 and AST-0228974.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.