Turbulent flows within self-gravitating magnetized molecular clouds

Self-gravitating magnetized flows are explored numerically in slab geometry. In this approximation, the derivatives are computed only in one dimension but all three components of vector fields are retained. This is done for a range of fiducial values for the interstellar medium at the scale of molecular clouds. The overall characteristic scale of the turbulence, its Mach number, and the initial ratio of longitudinal to transverse turbulent velocities, as well as the extent of the initial density bulges within the fluid, are the main parameters of the study. Simulations have been performed with and without ambipolar drift. No external forcing is included. Velocity, density, and magnetic perturbations develop self-consistently to comparable levels in all cases. This includes those cases where the medium is initially static. However, a fully random flow produces substantially more density contrast with nested substructures. Collapse eventually occurs after typically three free-fall times. The magnetic field slows down the collapse as expected. For higher Mach numbers, the collapse is faster, and yet the peak densities reached in the final collapsed objects are lower. We have also modeled the effects of ambipolar drift in the presence of cosmic ray ionization and far-ultraviolet ionization. Because the turbulent timescales are shorter than the ambipolar drift timescales, we find that ambipolar drift does not play a significant role in gravitational collapse in a turbulent medium of the type modeled in our simulations.