JCMT BISTRO Survey: Magnetic Fields within the Hub-filament Structure in IC 5146
Authors: Wang Jia-Wei , Lai Shih-Ping , Eswaraiah Chakali , Pattle Kate , Francesco James Di , Johnstone Doug , Koch Patrick M. , Liu Tie , Tamura Motohide , Furuya Ray S. , Onaka Takashi , Ward-Thompson Derek , Soam Archana , Kim Kee-Tae , Lee Chang Won , Lee Chin-Fei , Mairs Steve , Arzoumanian Doris , Kim Gwanjeong , Hoang Thiem , Hwang Jihye , Liu Sheng-Yuan , Berry David , Bastien Pierre , Hasegawa Tetsuo , Kwon Woojin , Qiu Keping , André Philippe , Aso Yusuke , Byun Do-Young , Chen Huei-Ru , Chen Michael C. , Chen Wen Ping , Ching Tao-Chung , Cho Jungyeon , Choi Minho , Chrysostomou Antonio , Chung Eun Jung , Coudé Simon , Doi Yasuo , Dowell C. Darren , Drabek-Maunder Emily , Duan Hao-Yuan , Eyres Stewart P. S. , Falle Sam , Fanciullo Lapo , Fiege Jason , Franzmann Erica , Friberg Per , Friesen Rachel K. , Fuller Gary , Gledhill Tim , Graves Sarah F. , Greaves Jane S. , Griffin Matt J. , Gu Qilao , Han Ilseung , Hatchell Jennifer , Hayashi Saeko S. , Holland Wayne , Houde Martin , Inoue Tsuyoshi , Inutsuka Shu-ichiro , Iwasaki Kazunari , Jeong Il-Gyo , Kanamori Yoshihiro , Kang Ji-hyun , Kang Miju , Kang Sung-ju , Kataoka Akimasa , Kawabata Koji S. , Kemper Francisca , Kim Jongsoo , Kim Kyoung Hee , Kim Mi-Ryang , Kim Shinyoung , Kirk Jason M. , Kobayashi Masato I. N. , Konyves Vera , Kwon Jungmi , Lacaille Kevin M. , Lee Hyeseung , Lee Jeong-Eun , Lee Sang-Sung , Lee Yong-Hee , Li Dalei , Li Di , Li Hua-bai , Liu Hong-Li , Liu Junhao , Lyo A-Ran , Matsumura Masafumi , Matthews Brenda C. , Moriarty-Schieven Gerald H. , Nagata Tetsuya , Nakamura Fumitaka , Nakanishi Hiroyuki , Ohashi Nagayoshi , Park Geumsook , Parsons Harriet , Pascale Enzo , Peretto Nicolas , Pon Andy , Pyo Tae-Soo , Qian Lei , Rao Ramprasad , Rawlings Mark G. , Retter Brendan , Richer John , Rigby Andrew , Robitaille Jean-François , Sadavoy Sarah , Saito Hiro , Savini Giorgio , Scaife Anna M. M. , Seta Masumichi , Shinnaga Hiroko , Tang Ya-Wen , Tomisaka Kohji , Tsukamoto Yusuke , Loo Sven van , Wang Hongchi , Whitworth Anthony P. , Yen Hsi-Wei , Yoo Hyunju , Yuan Jinghua , Yun Hyeong-Sik , Zenko Tetsuya , Zhang Chuan-Peng , Zhang Guoyin , Zhang Ya-Peng , Zhou Jianjun , Zhu Lei 
Published: May 2019

Abstract
We present the 850 μm polarization observations toward the IC 5146 filamentary cloud taken using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and its associated polarimeter (POL-2), mounted on the James Clerk Maxwell Telescope, as part of the B-fields In STar forming Regions Observations. This work is aimed at revealing the magnetic field morphology within a core-scale (≲1.0 pc) hub-filament structure (HFS) located at the end of a parsec-scale filament. To investigate whether the observed polarization traces the magnetic field in the HFS, we analyze the dependence between the observed polarization fraction and total intensity using a Bayesian approach with the polarization fraction described by the Rice likelihood function, which can correctly describe the probability density function of the observed polarization fraction for low signal-to-noise ratio data. We find a power-law dependence between the polarization fraction and total intensity with an index of 0.56 in A

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∼ 20–300 mag regions, suggesting that the dust grains in these dense regions can still be aligned with magnetic fields in the IC 5146 regions. Our polarization maps reveal a curved magnetic field, possibly dragged by the contraction along the parsec-scale filament. We further obtain a magnetic field strength of 0.5 ± 0.2 mG toward the central hub using the Davis–Chandrasekhar–Fermi method, corresponding to a mass-to-flux criticality of ∼1.3 ± 0.4 and an Alfvénic Mach number of <0.6. These results suggest that gravity and magnetic field are currently of comparable importance in the HFS and that turbulence is less important.