Observations of Magnetic Fields Surrounding LkHα 101 Taken by the BISTRO Survey with JCMT-POL-2

Abstract

We report the first high spatial resolution measurement of magnetic fields surrounding LkHα 101, a part of the Auriga-California molecular cloud. The observations were taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope within the framework of the B-fields In Star-forming Region Observations (BISTRO) survey. Observed polarization of thermal dust emission at 850 µm is found to be mostly associated with the red-shifted gas component of the cloud. The magnetic field displays a relatively complex morphology. Two variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure function, are used to calculate the strength of magnetic fields in the plane of the sky, yielding a similar result of B POS ∼ 115 µG. The mass-to-magnetic-flux ratio in critical value units, λ ∼ 0.3, is the smallest among the values obtained for other regions surveyed by POL-2. This implies that the LkHα 101 region is sub-critical and the magnetic field is strong enough to prevent gravitational collapse. The inferred δB/B 0 ∼ 0.3 implies that the large scale component of the magnetic field dominates the turbulent one. The variation of the polarization fraction with total emission intensity can be fitted by a power-law with an index of α = 0.82 ± 0.03, which lies in the range previously reported for molecular clouds. We find that the polarization fraction decreases rapidly with proximity to the only early B star (LkHα 101) in the region. The magnetic field tangling and the joint effect of grain alignment and rotational disruption by radiative torques are potential of explaining such a decreasing trend.

The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament

“…Our observations toward the DR21 filament are part of the extension of the B-fields In STar-forming Region Observations (BISTRO) survey (Ward-Thompson et al 2017). The BISTRO-1 survey carried out POL-2 observations from 2016 to 2019 toward nearby star-forming regions of the Gould Belt clouds, including Orion A (Pattle et al 2017;Hwang et al 2021), Ophiuchus (Kwon et al 2018;Soam et al 2018;Liu et al 2019), IC 5146 (Wang et al 2019), Barnard 1 (Coudé et al 2019), NGC 1333 (Doi et al 2020(Doi et al , 2021, Auriga (Ngoc et al 2021), Taurus (Eswaraiah et al 2021), Orion B (Lyo et al 2021), and Serpens (Kwon et al 2022), aiming to generate a large sample of polarization maps in a uniform and consistent way to study the role of magnetic fields in star formation at scales of a few thousand au. The BISTRO-1 survey was later extended to the BISTRO-2 program for high-mass star-forming regions (M16: Pattle et al 2018;Rosette: Könyves et al 2021;NGC 6334: Arzoumanian et al 2021;Mon R2: Hwang et al 2022) as well as to the ongoing BISTRO-3 program for various evolutionary stages and environments of star formation.…”

Three-dimensional magnetic fields of molecular clouds

“…Numerous observatories, including the James Clark Maxwell Telescope (JCMT; e.g., Eswaraiah et al, 2021;Ngoc et al, 2021;Hwang et al, 2021;Kwon et al, 2022), Planck Space Observatory (e.g., Planck Collaboration et al, 2016;Alina et al, 2019), Atacama Large Millimeter/sub-millimeter Array (ALMA; e.g., Pattle et al, 2021;Cortés et al, 2021), Sub-Millimeter Array (SMA; e.g., Zhang et al, 2014), and Stratospheric Observatory for Infrared Astronomy (SOFIA; e.g., Chuss et al, 2019) have observed B POS of numerous star-forming regions. However, the number of B LOS observations of molecular clouds are still limited.…”

Recent progress in theory and observational study of dust grain alignment and rotational disruption in star-forming regions

“…The variation of p with the total emission intensity (I) permits a popular analysis of polarimetric data to study the variation of grain alignment and magnetic field geometry across the observed region. The general trend observed toward molecular clouds is p ∝ I −α with the power-index α between 0 and 1 (e.g., Coudé et al, 2019;Ngoc et al, 2021). If the magnetic field is uniform, α = 0, indicating that grain alignment is uniform, whereas α = 1 implies that grain alignment only occurs in the outer layer of the cloud and becomes completely lost in the inner region (Whittet et al, 2008).…”

“…The authors demonstrated that the combination of the RAT-A and RAT-D effects could successfully reproduce the observational data. Since then, more observations have shown evidences for the RAT-D mechanism (e.g., Tram et al, 2021b;Ngoc et al, 2021;Hoang T. D. et al, 2022).…”