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