Formation and Collapse of Nonaxisymmetric Protostellar Cores in Planar Magnetic Molecular Clouds

We extend our earlier work on ambipolar diffusion-induced formation of protostellar cores in isothermal sheetlike magnetic interstellar clouds by studying nonaxisymmetric collapse for the physically interesting regime of magnetically critical and supercritical model clouds (μ₀ ≥ 1, where μ₀ is the initial mass-to-magnetic flux ratio in units of the critical value for gravitational collapse). Cores that form in model simulations are effectively triaxial, with shapes that are typically closer to being oblate rather than prolate. Infall velocities in the critical model (μ₀ = 1) are subsonic; in contrast, a supercritical model (μ₀ = 2) has extended supersonic infall that may be excluded by observations. For the magnetically critical model, ambipolar diffusion forms cores that are supercritical (μ_core > 1) and embedded within subcritical envelopes (μ_env < 1). Cores in our models have density profiles that eventually merge into a near-uniform background, which is suggestive of observed properties of cloud cores.