Line emission from filaments in molecular clouds

TL;DR

This study uses advanced simulations to predict the emission properties of filaments in molecular clouds, showing that their observed kinematic features can be explained by dynamic formation processes rather than equilibrium states.

Contribution

It demonstrates that dynamically forming filaments can reproduce observed emission and kinematic features, challenging equilibrium-based models.

Findings

Line widths are typically subsonic to transonic.

Simulations match observed emission properties.

Filaments form from supersonic inflows without equilibrium.

Abstract

Filamentary structures are often identified in column density maps of molecular clouds, and appear to be important for both low- and high-mass star formation. Theoretically, these structures are expected to form in regions where the supersonic cloud-scale turbulent velocity field converges. While this model of filament formation successfully reproduces several of their properties derived from column densities, it is unclear whether it can also reproduce their kinematic features. We use a combination of hydrodynamical, chemical and radiative transfer modelling to predict the emission properties of these dynamically-forming filaments in the $^{13}$CO, HCN and N$_2$H$^+$ $J=1-0$ rotational lines. The results are largely in agreement with observations; in particular, line widths are typically subsonic to transonic, even for filaments which have formed from highly supersonic inflows. If the observed filaments are formed dynamically, as our results suggest, no equilibrium analysis is possible, and simulations which presuppose the existence of a filament are likely to produce unrealistic results.