The widths of magnetised filaments in molecular clouds

TL;DR

This paper investigates how magnetic fields influence the widths of filaments in molecular clouds, showing that supercritical magnetic fields do not significantly alter the formation mechanism, while subcritical fields produce inconsistent widths.

Contribution

It demonstrates that magnetic fields with supercritical mass-to-flux ratios do not significantly change filament width distributions formed by turbulent flows, extending previous non-magnetic models.

Findings

Supercritical magnetic fields produce filament widths similar to non-magnetic models.

Subcritical magnetic fields lead to wider and differently shaped filament width distributions.

Filament widths are not strongly correlated with surface densities, consistent with observations.

Abstract

Filaments are an ubiquitous feature of molecular clouds, and appear to play a critical role in assembling the material to form stars. The dominant filaments are observed to have a rather narrow range of widths around $\sim 0.1$ pc, and to be preferentially aligned perpendicularly to the direction of the local magnetic field. We have previously argued that the observed filament widths can be explained if filaments are formed by converging, mildly supersonic flows, resulting from large-scale turbulent motions in the parent molecular cloud. Here we demonstrate that the introduction of a magnetic field perpendicular to the filament long axis does not greatly alter this conclusion, as long as the mass-to-flux ratio is supercritical. The distribution of widths for supercritical magnetised filaments formed via this mechanism is peaked at slightly higher values, and is slightly broader, than for non-magnetised filaments, but still reproduces the basic properties of the width distributions derived from far-infrared observations of molecular clouds. In contrast, subcritical filaments have width distributions with a fundamentally different shape, and typically have much larger widths than those observed. Both subcritical and supercritical filaments are consistent with the observed lack of correlation between filament widths and filament surface densities.