Sub-Alfvénic non-ideal magnetohydrodynamic turbulence simulations with ambipolar diffusion. III. Implications for observations and turbulent enhancement

Abstract

Ambipolar diffusion (AD) is believed to be a crucial process for redistributing magnetic flux in the dense molecular gas that occurs in regions of star formation. We carry out numerical simulations of this process in regions of low ionization using the heavy-ion approximation. The simulations are for regions of strong field (plasma β = 0.1) and mildly supersonic turbulence (M= 3, corresponding to an Alfv́en Mach number of 0.67). The velocity power spectrum of the neutral gas changes from an IroshnikovKraichnan spectrum in the case of ideal MHD to a Burgers spectrum in the case of a shock-dominated hydrodynamic system. The magnetic power spectrum shows a similar behavior. We use a one-dimensional radiative transfer code to post-process our simulation results; the simulated emission from the CS J = 21 and H13CO + J = 10 lines shows that the effects of AD are observable in principle. Linewidths of ions are observed to be less than those of neutrals, and we confirm previous suggestions that this is due to AD. We show that AD is unlikely to affect the ChandrasekharFermi method for inferring field strengths unless the AD is stronger than generally observed. Finally, we present a study of the enhancement of AD by turbulence, finding that AD is accelerated by factor 24.5 for non-self-gravitating systems with the level of turbulence we consider.