Magnetic Fields toward Ophiuchus-B Derived from SCUBA-2 Polarization Measurements

Archana Soam ,Anthony Peter Whitworth ,Hiro Saito ,Jennifer Hatchell ,J M Kirk ,Doug Johnstone ,Mi-Ryang Kim ,Yasuo Doi ,Jinghua Yuan ,Hiroyuki Nakanishi ,Jeong Eun Lee ,Shu‐Ichiro Inutsuka ,G A Fuller ,Yoshihiro Kanamori ,Kee‐Tae Kim ,Mike C.-Y Chen ,S P S Eyres ,Tsuyoshi Inoue ,Nagayoshi Ohashi ,Lei Zhu ,Sheng-Yuan Liu ,G H Moriarty‐Schieven ,Shinyoung Kim ,W S Holland ,Ramprasad Rao ,Takashi Onaka ,Il-Gyo Jeong ,D Arzoumanian ,A Chrysostomou ,Andy Pon ,Jean-Franois Robitaille ,Masato I N Kobayashi ,Koji S Kawabata ,Kyoung Hee Kim ,Hongchi Wang ,Hua-Bai Li ,P André ,Minho Choi ,Chuan-Peng Zhang ,Jason D Fiege ,James Di Francesco ,Akimasa Kataoka ,F Kemper ,Andrew Rigby ,Hiroko Shinnaga ,Miju Kang ,Di Li ,Hongli Liu ,Tim Gledhill ,Jihye Hwang ,Matt Griffin ,Jianjun Zhou ,Hsi-Wei Yen ,Tie Liu ,Kohji Tomisaka ,Ray S Furuya ,Derek Ward-Thompson ,Jong-Soo Kim ,Lei Qian ,Yusuke Aso ,Fúmitaka Nakamura ,E Drabek-Maunder ,Kate Pattle ,Per Friberg ,Erica Franzmann ,Brendan Retter ,Dalei Li ,Mark G Rawlings ,A-Ran Lyo ,Martin Houde ,Sang-Sung Lee ,Jungyeon Cho ,Keping Qiu ,T Nagata ,Brenda C Matthews ,N Peretto ,Sarah Sadavoy ,Anna M M Scaife ,Qilao Gu ,Tetsuo Hasegawa ,D S Berry ,Jiawei Wang ,Jungmi Kwon ,Tae‐Soo Pyo ,Sarah Graves ,Pierre Bastien ,Saeko S Hayashi ,Thiem Hoang ,Guoyin Zhang ,Hyunju Yoo ,C D Dowell ,Huei-Ru Vivien Chen ,Patrick M Koch ,Shih-Ping Lai ,Doyoung Byun ,Masatoshi Matsumura ,Ji-Hyun Kang ,Motohide Tamura ,J S Richer ,Junhao Liu ,Kazunari Iwasaki ,Ya-Wen Tang ,Rachel Friesen ,Sung-Ju Kang ,Masumichi Seta ,Simon Coudé ,J S Greaves ,Ilseung Han ,G Savini ,Harriet Parsons ,Kevin Lacaille ,Woojin Kwon ,Hyeseung Lee ,Chang Won Lee ,Wen-Ping Chen ,S A E G Falle ,Steve Mairs ,Eun Jung Chung ,Yusuke Tsukamoto ,S Van Loo ,Tao-Chung Ching ,Gwanjeong Kim ,Chakali Eswaraiah ,Tetsuya Zenko

doi:10.3847/1538-4357/aac4a6

Abstract

Abstract We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope in Hawaii. This work is part of the B-fields in Star-forming Region Observations survey initiated to understand the role of magnetic fields in star formation for nearby star-forming molecular clouds. We present a first look at the geometry and strength of magnetic fields in Oph-B. The field geometry is traced over ∼0.2 pc, with clear detection of both of the sub-clumps of Oph-B. The field pattern appears significantly disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered, with a tendency to be along the major axis of the clump, parallel to the filamentary structure within which it lies. The degree of polarization decreases systematically toward the dense core material in the two sub-clumps. The field lines in the lower density material along the periphery are smoothly joined to the large-scale magnetic fields probed by NIR polarization observations. We estimated a magnetic field strength of 630 ± 410 μG in the Oph-B2 sub-clump using a Davis–Chandrasekhar–Fermi analysis. With this magnetic field strength, we find a mass-to-flux ratio λ = 1.6 ± 1.1, which suggests that the Oph-B2 clump is slightly magnetically supercritical.

Highlights

Low mass stars are formed in dense cores (M ≈ 1 − 10 M⊙, size≈0.1-0.4 pc and density ≈ 104 − 105cm−3) embedded in molecular clouds which are generally selfgravitating, turbulent, magnetized and thought to be compressible fluids and are expected to form one or a few stars when they become unstable to gravitational collapse.Considering the magnetized nature of molecular clouds (Shu et al, 1987; McKee & Ostriker, 2007), we expect magnetic fields (B-fields) to have a significant impact on dense cores
We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope (JCMT) in Hawaii
We present the first submm polarization observations made using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with the POL-2 polarimeter towards the Oph-B region to map the B-fields on core scales

Summary

Introduction

Low mass stars are formed in dense cores (M ≈ 1 − 10 M⊙, size≈0.1-0.4 pc and density ≈ 104 − 105cm−3) embedded in molecular clouds which are generally selfgravitating, turbulent, magnetized and thought to be compressible fluids and are expected to form one or a few stars when they become unstable to gravitational collapse.Considering the magnetized nature of molecular clouds (Shu et al, 1987; McKee & Ostriker, 2007), we expect magnetic fields (B-fields) to have a significant impact on dense cores. Isolated low-mass cores that are magnetically dominated may gradually condense out of a large scale cloud through ambipolar diffusion (e.g., Shu et al, 1987; McKee et al, 1993; Mouschovias & Ciolek, 1999; Allen et al, 2003). In this picture, the core will be flattened into a disk-like morphology on scales of a few thousand AU, with field lines primarily parallel to the symmetry axis. In this picture the Bfield morphology will be more chaotic (Crutcher, 2004; Hull et al, 2017a)

Results

Discussion

Conclusion