Fragmentation Instability of Molecular Clouds: Numerical Simulations

We simulate fragmentation and gravitational collapse of cold, magnetizedmolecular clouds. We explore the nonlinear development of an instabilitymediated by ambipolar diffusion, in which the collapse rate is intermediate tofast gravitational collapse and slow quasistatic collapse. Initially uniformstable clouds fragment into elongated clumps with masses largely determined bythe cloud temperature, but substantially larger than the thermal Jeans mass.The clumps are asymmetric, with significant rotation and vorticity, and losemagnetic flux as they collapse. The clump shapes, intermediate collapse rates,and infall profiles may help explain observations not easily fit bycontemporary slow or rapid collapse models.Comment: 25pp, 20 small eps figures, in press ApJ, April 1, 200