OMC-1 dust polarization in ALMA Band 7: diagnosing grain alignment mechanisms in the vicinity of Orion Source I

Author:

Pattle Kate12ORCID,Lai Shih-Ping23ORCID,Wright Melvyn4ORCID,Coudé Simon5ORCID,Plambeck Richard4ORCID,Hoang Thiem67ORCID,Tang Ya-Wen3ORCID,Bastien Pierre8ORCID,Eswaraiah Chakali9ORCID,Furuya Ray S10ORCID,Hwang Jihye67ORCID,Inutsuka Shu-ichiro11ORCID,Kim Kee-Tae67ORCID,Kirchschlager Florian12ORCID,Kwon Woojin136ORCID,Lee Chang Won67ORCID,Liu Sheng-Yuan3ORCID,Lyo Aran6ORCID,Ohashi Nagayoshi3ORCID,Rawlings Mark G14ORCID,Tahani Mehrnoosh15ORCID,Tamura Motohide161718ORCID,Soam Archana5ORCID,Wang Jia-Wei3ORCID,Ward-Thompson Derek19ORCID

Affiliation:

1. Centre for Astronomy, Department of Physics, National University of Ireland Galway, University Road, Galway H91 TK33, Ireland

2. Institute of Astronomy, Department of Physics, National Tsing Hua University, No. 101, Section 2 Guangfu Road, Hsinchu 30013, Taiwan

3. Academia Sinica Institute of Astronomy and Astrophysics, No. 1, Section 4 Roosevelt Road, Taipei 10617, Taiwan

4. Radio Astronomy Lab, University of California, 501 Campbell Hall, Berkeley CA 94720-3441, USA

5. SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, Moffett Field, CA 94035, USA

6. Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea

7. University of Science and Technology, Korea, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea

8. Centre de recherche en astrophysique du Québec & département de physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC, H3C 3J7, Canada

9. CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 10012, People’s Republic of China

10. Institute of Liberal Arts and Sciences, Tokushima University, Minami Jousanajima-machi 1-1, Tokushima 770-8502, Japan

11. Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan

12. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

13. Department of Earth Science Education, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

14. East Asian Observatory, 660 N. A’ohōkū Place, University Park, Hilo, HI 96720, USA

15. Dominion Radio Astrophysical Observatory, Herzberg Astronomy and Astrophysics Research Centre, National Research Council Canada, P. O. Box 248, Penticton, BC V2A 6J9 Canada

16. National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Osawa, Mitaka, Tokyo 181-8588, Japan

17. Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

18. Astrobiology Center, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

19. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK

Abstract

ABSTRACT We present ALMA Band 7 polarization observations of the OMC-1 region of the Orion molecular cloud. We find that the polarization pattern observed in the region is likely to have been significantly altered by the radiation field of the >104 L⊙ high-mass protostar Orion Source I. In the protostar’s optically thick disc, polarization is likely to arise from dust self-scattering. In material to the south of Source I – previously identified as a region of ‘anomalous’ polarization emission – we observe a polarization geometry concentric around Source I. We demonstrate that Source I’s extreme luminosity may be sufficient to make the radiative precession time-scale shorter than the Larmor time-scale for moderately large grains ($\gt 0.005\!-\!0.1\, \mu$m), causing them to precess around the radiation anisotropy vector (k-RATs) rather than the magnetic field direction (B-RATs). This requires relatively unobscured emission from Source I, supporting the hypothesis that emission in this region arises from the cavity wall of the Source I outflow. This is one of the first times that evidence for k-RAT alignment has been found outside of a protostellar disc or AGB star envelope. Alternatively, the grains may remain aligned by B-RATs and trace gas infall on to the Main Ridge. Elsewhere, we largely find the magnetic field geometry to be radial around the BN/KL explosion centre, consistent with previous observations. However, in the Main Ridge, the magnetic field geometry appears to remain consistent with the larger-scale magnetic field, perhaps indicative of the ability of the dense Ridge to resist disruption by the BN/KL explosion.

Funder

National Science Foundation

National Institutes of Natural Sciences

National Research Council Canada

Ministry of Science and Technology

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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