Non-Ideal Magnetohydrodynamic Simulations of the Two-Stage Fragmentation Model for Cluster Formation

Abstract

We model molecular cloud fragmentation with thin disk non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and partial ionization that transitions from primarily ultraviolet dominated to cosmic ray dominated regimes. These simulations are used to determine the conditions required for star clusters to form through a two-stage fragmentation scenario. Recent linear analyses have shown that the fragmentation length and time scales can undergo a dramatic drop across the column density boundary that separates the ultraviolet and cosmic ray dominated ionization regimes. As found in earlier studies, the absence of an ionization drop and regular perturbations leads to a single-stage fragmentation on parsec scales in transcritical clouds, so that the nonlinear evolution yields the same fragment sizes as predicted by linear theory. However, we find that a combination of initial transcritical mass-to-flux ratio, evolution through a column density regime in which the ionization drop takes place, and regular small perturbations to the mass-to-flux ratio are sufficient to cause a second stage of fragmentation during the nonlinear evolution. Cores of size ~0.1 pc are formed within an initial fragment of ~ pc size. Regular perturbations to the mass-to-flux ratio also accelerate the onset of runaway collapse.

12 pages, 6 figures, 4 tables. Accepted for publication in ApJ

References in corpus (5)

• The relation between gas and dust in the Taurus Molecular Cloud
• The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
• Current Star Formation in the Perseus Molecular Cloud: Constraints from Unbiased Submillimeter and Mid-Infrared Surveys
• Nonlinear Evolution of Gravitational Fragmentation Regulated by Magnetic Fields and Ambipolar Diffusion
• Ambipolar Diffusion in Molecular Cloud Cores and the Gravomagneto Catastrophe

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