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2017ApJ...846..122P - Astrophys. J., 846, 122-122 (2017/September-2)

The JCMT BISTRO survey: the magnetic field strength in the Orion A filament.

PATTLE K., WARD-THOMPSON D., BERRY D., HATCHELL J., CHEN H.-R., PON A., KOCH P.M., KWON W., KIM J., BASTIEN P., CHO J., COUDE S., DI FRANCESCO J., FULLER G., FURUYA R.S., GRAVES S.F., JOHNSTONE D., KIRK J., KWON J., LEE C.W., MATTHEWS B.C., MOTTRAM J.C., PARSONS H., SADAVOY S., SHINNAGA H., SOAM A., HASEGAWA T., LAI S.-P., QIU K. and FRIBERG P.

Abstract (from CDS):

We determine the magnetic field strength in the OMC 1 region of the Orion A filament via a new implementation of the Chandrasekhar-Fermi method using observations performed as part of the James Clerk Maxwell Telescope (JCMT) B-Fields In Star-forming Region Observations (BISTRO) survey with the POL-2 instrument. We combine BISTRO data with archival SCUBA-2 and HARP observations to find a plane-of-sky magnetic field strength in OMC 1 of Bpos=6.6±4.7 mG, where δBpos=4.7 mG represents a predominantly systematic uncertainty. We develop a new method for measuring angular dispersion, analogous to unsharp masking. We find a magnetic energy density of ∼1.7×10–7 J m–3 in OMC 1, comparable both to the gravitational potential energy density of OMC 1 (∼10–7 J m–3) and to the energy density in the Orion BN/KL outflow (∼10–7 J m–3). We find that neither the Alfven velocity in OMC 1 nor the velocity of the super-Alfvenic outflow ejecta is sufficiently large for the BN/KL outflow to have caused large-scale distortion of the local magnetic field in the ∼500 yr lifetime of the outflow. Hence, we propose that the hourglass field morphology in OMC 1 is caused by the distortion of a primordial cylindrically symmetric magnetic field by the gravitational fragmentation of the filament and/or the gravitational interaction of the BN/KL and S clumps. We find that OMC 1 is currently in or near magnetically supported equilibrium, and that the current large-scale morphology of the BN/KL outflow is regulated by the geometry of the magnetic field in OMC 1, and not vice versa.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): ISM: individual objects: OMC 1 - magnetic fields - techniques: polarimetric - stars: formation - stars: formation

Simbad objects: 12

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