JCMT BISTRO Survey: Magnetic Fields within the Hub-filament Structure in IC 5146

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 V ∼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.

The JCMT BISTRO Survey: Magnetic Fields Associated with a Network of Filaments in NGC 1333

“…This survey is designed to cover a variety of nearby star-forming regions, with an initial focus on the Gould Belt molecular clouds. The regions published so far are Orion A (Pattle et al 2017), M16 (Pattle et al 2018), ρ Ophiuchus A (Kwon et al 2018), ρ Ophiuchus B (Soam et al 2018), ρ Ophiuchus C (Liu et al 2019), Perseus B1 (Coudé et al 2019), and IC 5146 (Wang et al 2019). In this paper, we present new observational results of the NGC 1333 star-forming region in the Perseus molecular cloud obtained by the BISTRO survey.…”

Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions

“…It should be noted that the standard selection of polarization vectors by their signal-to-noise ratio in polarization fraction, p/δp may create bias in the recovered value of α. The sensitivity of recent observations allows the implementation of Bayesian analyses of the ǫ p -A V relationship (Wang et al, 2018), which should better inform future discussions of the limits of applicability of submillimeter polarization observations.…”

The JCMT BISTRO Survey: The Magnetic Field of the Barnard 1 Star-forming Region

“…In Section 4.2, we also find a plane-of-sky amplitude B pos =120±60 μG for the magnetic field and a criticality criterion λ c =3.0±1.5. Although this magnetic field amplitude is relatively weak when compared to the fields found in high-mass star-forming regions such as OrionA (where B pos 1.0 mG; e.g., Houde et al 2009;Pattle et al 2017) or in hub-filament structures such as IC5146 (with B pos ∼0.5 mG; e.g., Wang et al 2019), it is either comparable to or larger than the field strengths (B pos 100 μG) typically found in low-mass prestellar cores (e.g., Crutcher et al 2004;Kirk et al 2006;Liu et al 2019). Above all, these results indicate that Perseus B1 is a supercritical molecular cloud (i.e., magnetic pressure alone cannot support the cloud against gravity).…”