The widths of magnetised filaments in molecular clouds

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 ∼ 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.

Supervised machine learning on Galactic filaments

“…Because filaments host star formation and link the organization of the interstellar matter to the future star formation, studying them is central to our understanding of all properties related to star formation, such as the initial mass function, the star formation rate, and the star formation efficiency. Filaments are therefore extensively studied with observations at all wavelengths and numerical simulations (André et al 2010;Molinari et al 2010;Arzoumanian et al 2011;Hacar et al 2018;Arzoumanian et al 2019;Shimajiri et al 2019;Clarke et al 2020;Priestley & Whitworth 2022;Hacar et al 2022, and references therein). All these data reveal the complex structure of filaments and show a chang-⋆ F.-X.…”