Magnetically Dominated Parallel Interstellar Filaments at the Infrared Dark Cloud G14.225-0.506

TL;DR

This study reveals that strong magnetic fields in the IRDC G14.2 shape its parallel filamentary structure and influence its collapse dynamics, supported by polarimetric observations and numerical simulations.

Contribution

The paper provides the first detailed polarimetric mapping of magnetic fields in IRDC G14.2, demonstrating their dominant role in filament formation and cloud evolution.

Findings

Magnetic fields are perpendicular to filament orientations.

Magnetic field strengths are estimated between 320-550 μG.

The cloud's contraction timescale exceeds free-fall predictions.

Abstract

The G14.225-0.506 infrared dark cloud (IRDC G14.2) displays a remarkable complex of parallel dense molecular filaments projected on the plane of the sky. Previous dust emission and molecular-line studies have speculated whether magnetic fields could have played an important role in the formation of such long-shaped structures, which are hosts to numerous young stellar sources. In this work we have conducted a vast polarimetric survey at optical and near-infrared wavelengths in order to study the morphology of magnetic field lines in IRDC G14.2 through the observation of background stars. The orientation of interstellar polarization, which traces magnetic field lines, is perpendicular to most of the filamentary features within the cloud. Additionally, the larger-scale molecular cloud as a whole exhibits an elongated shape also perpendicular to magnetic fields. Estimates of magnetic field strengths indicate values in the range $320 - 550\,\mu$G, which allows sub-alfv\'enic conditions, but does not prevent the gravitational collapse of hub-filament structures, which in general are close to the critical state. These characteristics suggest that magnetic fields played the main role in regulating the collapse from large to small scales, leading to the formation of series of parallel elongated structures. The morphology is also consistent with numerical simulations that show how gravitational instabilities develop under strong magnetic fields. Finally, the results corroborate the hypothesis that a strong support from internal magnetic fields might explain why the cloud seems to be contracting on a time scale 2-3 times larger than what is expected from a free-fall collapse.