The CARMA-NRO Orion Survey: Filament Formation via Collision-Induced Magnetic Reconnection -- The Stick in Orion A

TL;DR

This study identifies a unique, straight filament in Orion A formed by collision-induced magnetic reconnection, demonstrating a rapid dense gas formation process through MHD simulations, with implications for star formation.

Contribution

The paper presents the first observational evidence and MHD simulation of filament formation via collision-induced magnetic reconnection in a giant molecular cloud.

Findings

The filament, named the Stick, is ruler-straight and at an early evolutionary stage.

Collision-induced magnetic reconnection rapidly produces dense filaments with high density contrast.

Magnetic reconnection accelerates dense gas formation, surpassing free-fall collapse timescales.

Abstract

A unique filament is identified in the {\it Herschel} maps of the Orion A giant molecular cloud. The filament, which, we name the Stick, is ruler-straight and at an early evolutionary stage. Transverse position-velocity diagrams show two velocity components closing in on the Stick. The filament shows consecutive rings/forks in C$^{18}$O(1-0) channel maps, which is reminiscent of structures generated by magnetic reconnection. We propose that the Stick formed via collision-induced magnetic reconnection (CMR). We use the magnetohydrodynamics (MHD) code Athena++ to simulate the collision between two diffuse molecular clumps, each carrying an anti-parallel magnetic field. The clump collision produces a narrow, straight, dense filament with a factor of $>$200 increase in density. The production of the dense gas is seven times faster than free-fall collapse. The dense filament shows ring/fork-like structures in radiative transfer maps. Cores in the filament are confined by surface magnetic pressure. CMR can be an important dense-gas-producing mechanism in the Galaxy and beyond.