by Nickolas Moeckel
The classical picture of a star-forming filament is a near-equilibrium structure, with collapse dependent on its gravitational criticality. Recent observations have complicated this picture, revealing filaments as a mess of apparently interacting subfilaments, with transsonic internal velocity dispersions and mildly supersonic intra-subfilament dispersions. How structures like this form is unresolved. We simulated a 10pc region of a turbulent molecular cloud, allowing it to evolve under self gravity for 1.25 Myr. While the global structure of the region is still dominated by its turbulent structure, the denser gas has had time to become gravitationally organized. We treated the simulation as an observer might observe the sky; converting the density to an approximate line intensity, selecting filamentary regions for further study, and analysing the line-of-sight velocity information in these regions. Our main finding is that velocity characteristics very similar to those observed form naturally in such a turbulent setup. Individually bound subfilaments display approximately sonic or subsonic dispersions, while the agglomerations that make up the larger filaments have transsonic to mildly supersonic relative motions. While we will further study the detailed evolution of these structures in future work, we speculate that this velocity structure is a relic of the supersonic turbulence that is generally taken as the initial conditions of star formation. The substructured (both in space and velocity) filaments appear without the need for magnetic fields, which are the physical mechanism that immediately spring to mind when considering a filament composed of a bundle of subfilaments. The figure shows one of the filamentary features in our simulation, with the column density in the bottom panel and the intertwining line-of-sight velocity feature in the upper panel.
The corresponding paper can be found here: http://adsabs.harvard.edu/abs/2014arXiv1402.2614M
and an interactive version of one of the figures is available here: http://nickolas1.com/filamentvelocities/