B -fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). VI. Grain Alignment Mechanisms in the Massive Quiescent Filament G16.96+0.27 Using Dust Polarization Observations from JCMT/POL-2
The Astrophysical Journal Supplement Series, vol. 283, pp. 65
Abstract
Abstract Dust polarization induced by aligned nonspherical grains acts as an important tool to trace the magnetic field ( B -field) morphologies and strengths in molecular clouds and constrain grain properties and their alignment mechanisms. The widely accepted grain alignment theory is the alignment induced by radiative torques (RATs). In this work, we investigate grain alignment mechanisms in a massive, quiescent and filamentary infrared dark cloud G16.96+0.27 using thermal dust polarization observation with JCMT/POL-2 at 850 μ m. We observe the so-called phenomenon of a polarization hole attributed to the decrease in polarization fraction in denser regions of higher total intensity and gas density. Our study finds that the B -field tangling effect is a minor cause of the polarization hole, and the dominant factor is the reduction in grain alignment efficiency in denser regions, consistent with the RAT mechanism. To test RAT theory, we calculate various quantities describing grain alignment, including the minimum size of aligned grains, magnetic and magnetic relaxation parameters, and show that the RAT mechanism can explain observational data. Our study also reveals evidence for a magnetically enhanced RAT (M-RAT) mechanism required to explain the observed high polarization fractions of above 10% in the outer regions of the filament. Finally, we perform detailed modeling of thermal dust polarization using DustPOL _ py based on M-RAT theory and find that the modeling could successfully reproduce the observational data when the maximum grain size is around 0.45 μ m accompanied by an increase in grain axial ratio, along with the consideration of variations in the magnetic field’s inclination angle with the line of sight.
Authors 8
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Indian Institute of Astrophysics · Pondicherry University
Affiliation as printed
Indian Institute of Astrophysics, II Block, Koramangala, 560034, India; saikhom.singh@iiap.res.in, spravash11@gmail.com
Pondicherry University, R.V. Nagar, Kalapet, Puducherry, 605014, India
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Korea Astronomy and Space Science Institute · Korea University of Science and Technology
Affiliation as printed
Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
University of Science and Technology, Korea, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
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Indian Institute of Astrophysics · Pondicherry University
Affiliation as printed
Indian Institute of Astrophysics, II Block, Koramangala, 560034, India; saikhom.singh@iiap.res.in, spravash11@gmail.com
Pondicherry University, R.V. Nagar, Kalapet, Puducherry, 605014, India
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Chinese Academy of Sciences · Shanghai Astronomical Observatory
Affiliation as printed
Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Xuhui, Shanghai 200030, People’s Republic of China
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Chinese Academy of Sciences · Shanghai Astronomical Observatory
Affiliation as printed
Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Xuhui, Shanghai 200030, People’s Republic of China
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Graduate University of Science and Technology · Trung tâm Vũ trụ Việt Nam · Vietnam Academy of Science and Technology
Affiliation as printed
Center for Astrophysics and Science Exploration, Vietnam National Space Center, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Graduate University of Science and Technology · Trung tâm Vũ trụ Việt Nam · Vietnam Academy of Science and Technology
Affiliation as printed
Center for Astrophysics and Science Exploration, Vietnam National Space Center, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
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