FORMATION OF MAGNETIZED PRESTELLAR CORES WITH AMBIPOLAR DIFFUSION AND TURBULENCE

Abstract

We investigate the roles of magnetic fields and ambipolar diffusion during\nprestellar core formation in turbulent giant molecular clouds (GMCs), using\nthree-dimensional numerical simulations. Our simulations focus on the shocked\nlayer produced by a converging flow within a GMC, and survey varying ionization\nand angle between the upstream flow and magnetic field. We also include ideal\nmagnetohydrodynamic (MHD) and hydrodynamic models. From our simulations, we\nidentify hundreds of self-gravitating cores that form within 1 Myr, with masses\nM ~ 0.04 - 2.5 solar-mass and sizes L ~ 0.015 - 0.07 pc, consistent with\nobservations of the peak of the core mass function (CMF). Median values are M =\n0.47 solar-mass and L = 0.03 pc. Core masses and sizes do not depend on either\nthe ionization or upstream magnetic field direction. In contrast, the\nmass-to-magnetic flux ratio does increase with lower ionization, from twice to\nfour times the critical value. The higher mass-to-flux ratio for low ionization\nis the result of enhanced transient ambipolar diffusion when the shocked layer\nfirst forms. However, ambipolar diffusion is not necessary to form low-mass\nsupercritical cores. For ideal MHD, we find similar masses to other cases.\nThese masses are 1 - 2 orders of magnitude lower than the value that defines a\nmagnetically supercritical sphere under post-shock ambient conditions. This\ndiscrepancy is the result of anisotropic contraction along field lines, which\nis clearly evident in both ideal MHD and diffusive simulations. We interpret\nour numerical findings using a simple scaling argument which suggests that\ngravitationally critical core masses will depend on the sound speed and mean\nturbulent pressure in a cloud, regardless of magnetic effects.\n