Magnetized interstellar molecular clouds – II. The large-scale structure and dynamics of filamentary molecular clouds

• Published in: Monthly notices of the Royal Astronomical Society Vol. 485; no. 4; pp. 4509 - 4528
• Main Authors: Li, Pak Shing, Klein, Richard I
• Format: Journal Article
• Language: English
• Published: United Kingdom Oxford University Press 01-06-2019
• Subjects: ISM: clouds; turbulence; methods: numerical; ISM: evolution; ISM: kinematics and dynamics; ISM: magnetic fields
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stz653

Abstract
We perform ideal magnetohydrodynamics high-resolution adaptive mesh refinement simulations with driven turbulence and self-gravity and find that long filamentary molecular clouds are formed at the converging locations of large-scale turbulence flows and the filaments are bounded by gravity. The magnetic field helps shape and reinforce the long filamentary structures. The main filamentary cloud has a length of ∼4.4 pc. Instead of a monolithic cylindrical structure, the main cloud is shown to be a collection of fibre/web-like substructures similar to filamentary clouds such as L1495. Unless the line-of-sight is close to the mean field direction, the large-scale magnetic field and striations in the simulation are found roughly perpendicular to the long axis of the main cloud, similar to L1495. This provides strong support for a large-scale moderately strong magnetic field surrounding L1495. We find that the projection effect from observations can lead to incorrect interpretations of the true three-dimensional physical shape, size, and velocity structure of the clouds. Helical magnetic field structures found around filamentary clouds that are interpreted from Zeeman observations can be explained by a simple bending of the magnetic field that pierces through the cloud. We demonstrate that two dark clouds form a T-shaped configuration that is strikingly similar to the infrared dark cloud SDC13, leading to the interpretation that SDC13 results from a collision of two long filamentary clouds. We show that a moderately strong magnetic field (${{\cal M}_{\rm A}}\sim 1$) is crucial for maintaining a long and slender filamentary cloud for a long period of time ∼0.5 Myr.