The JCMT BISTRO Survey: The Magnetic Field Strength in the Orion A Filament

Journal Article · Sun Sep 10 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA80E5· OSTI ID:22875828

Pattle, Kate; Ward-Thompson, Derek; Kirk, Jason ^[1]; Berry, David; Graves, Sarah F. ^[2]; Hatchell, Jennifer ^[3]; Chen, Huei-Ru ^[4]; Pon, Andy ^[5]; Koch, Patrick M. ^[6]; Kwon, Woojin; Kim, Jongsoo ^[7]; Bastien, Pierre; Coudé, Simon ^[8]; Cho, Jungyeon ^[9]; Di Francesco, James; Johnstone, Doug ^[10]; Fuller, Gary ^[11]; others, and

---

1. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom)
2. East Asian Observatory, 660 N. A’ohōkū Place, University Park, Hilo, HI 96720 (United States)
3. Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
4. Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
5. Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7 (Canada)
6. Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)
7. Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055 (Korea, Republic of)
8. Centre de recherche en astrophysique du Québec and département de physique, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada)
9. Department of Astronomy and Space Science, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134 (Korea, Republic of)
10. NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC V9E 2E7 (Canada)
11. Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)

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 B{sub pos}=6.6±4.7 mG, where δB{sub pos}=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{sup −7} J m{sup −3} in OMC 1, comparable both to the gravitational potential energy density of OMC 1 (∼10{sup −7} J m{sup −3}) and to the energy density in the Orion BN/KL outflow (∼10{sup −7} J m{sup −3}). We find that neither the Alfvén velocity in OMC 1 nor the velocity of the super-Alfvénic 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.

• OSTI ID: 22875828
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 846; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
DISPERSIONS
ENERGY DENSITY
GRAVITATIONAL INTERACTIONS
MAGNETIC FIELDS
STAR EVOLUTION
STARS
SYMMETRY
TELESCOPES
VELOCITY