Dense Gas Formation via Collision-induced Magnetic Reconnection in a Disk Galaxy with a BiSymmetric Spiral Magnetic Field

Abstract

Recently, a collision-induced magnetic reconnection (CMR) mechanism was proposed to explain a dense filament formation in the Orion A giant molecular cloud. A natural question is that whether CMR works elsewhere in the Galaxy. As an initial attempt to answer the question, this paper investigates the triggering of CMR and the production of dense gas in a flat-rotating disk with a modified BiSymmetric Spiral (BSS) magnetic field. Cloud-cloud collisions at field reversals in the disk are modeled with the Athena++ code. Under the condition that is representative of the warm neutral medium, the cloud-cloud collision successfully triggers CMR at different disk radii. However, dense gas formation is hindered by the dominating thermal pressure, unless a moderately stronger initial field $\gtrsim 5\mu$G is present. The strong-field model, having a larger Lundquist number $S_L$ and lower plasma $\beta$, activates the plasmoid instability in the collision midplane, which is otherwise suppressed by the disk rotation. We speculate that CMR can be common if more clouds collide along field reversals. However, to witness the CMR process in numerical simulations, we need to significantly resolve the collision midplane with a spatial dynamic range $\gtrsim 10^6$. If Milky Way spiral arms indeed coincide with field reversals in BSS, it is possible that CMR creates or maintains dense gas in the arms. High-resolution, high-sensitivity Zeeman/Faraday-Rotation observations are crucial for finding CMR candidates that have helical fields.

21 pages, 11 figures, 1 table, accepted by ApJ

References in corpus (12)

• The NumPy array: a structure for efficient numerical computation
• Instability of current sheets and formation of plasmoid chains
• The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
• General Theory of the Plasmoid Instability
• Magnetic field amplification in turbulent astrophysical plasmas
• Magnetic reconnection in the era of exascale computing and multiscale experiments
• Cloud-cloud collisions and triggered star formation
• Plasmoid Instability in Forming Current Sheets
• Magnetic fields in the Milky Way from pulsar observations: effect of the correlation between thermal electrons and magnetic fields
• The relative orientation between the magnetic field and gas density structures in non-gravitating turbulent media
• Connection among environment, cloud-cloud collision speed, and star formation activity in the strongly barred galaxy NGC1300
• The CARMA-NRO Orion Survey: Filament Formation via Collision-Induced Magnetic Reconnection -- The Stick in Orion A

Cited by in corpus (3)

• Filament Formation via Collision-induced Magnetic Reconnection -- Formation of a Star Cluster
• Superposing the Magnetic spiral structure of the Milky Way, on the stellar spiral arms -- Matching the unique galactic magnetic field reversal Zone with two galactic spiral arm Segments
• CMR exploration I -- filament structure with synthetic observations