Ambipolar Diffusion Heating in Turbulent Systems

TL;DR

This paper investigates ambipolar diffusion heating in turbulent molecular clouds through simulations, revealing it accounts for about 70% of turbulent dissipation and significantly influences energy dissipation scales.

Contribution

The study provides the first detailed simulation-based analysis of ambipolar diffusion heating rates and their impact on turbulent energy dissipation in molecular clouds.

Findings

Approximately 70% of turbulent dissipation is due to AD heating.

AD heating affects the energy dissipation length scale, reducing energy reaching small scales.

A relation for AD heating rate matching simulations within a factor of two is derived.

Abstract

The temperature of the gas in molecular clouds is a key determinant of the characteristic mass of star formation. Ambipolar diffusion (AD) is considered one of the most important heating mechanisms in weakly ionized molecular clouds. In this work, we study the AD heating rate using 2-fluid turbulence simulations and compare it with the overall heating rate due to turbulent dissipation. We find that for observed molecular clouds, which typically have Alfven Mach numbers of ~1 (Crutcher 1999) and AD Reynolds numbers of ~20 (McKee et al. 2010), about 70% of the total turbulent dissipation is in the form of AD heating. AD has an important effect on the length scale where energy is dissipated: when AD heating is strong, most of the energy in the cascade is removed by ion-neutral drift, with a comparatively small amount of energy making it down to small scales. We derive a relation for the AD heating rate that describes the results of our simulations to within a factor of two. Turbulent dissipation, including AD heating, is generally less important that cosmic-ray heating in molecular clouds, although there is substantial scatter in both.