First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

Abstract

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions thatthe survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC1 region. We see that the magnetic field lies approximately perpendicular to the famous "integral filament" in the densest regions of that filament. Furthermore, we see an "hourglass" magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

Hierarchical structure of the interstellar molecular clouds and star formation

“…Analysis of the observations has shown that the filaments may have a nearly constant radius ∼ 0.1 pc. Polarimetry surveys of the Gould belt indicated that the large-scale magnetic field direction can be both perpendicular and parallel to the axis of a filament (Ward-Thompson et al 2017). These findings rise a question how the different filaments form.…”

The JCMT BISTRO Survey: The Magnetic Field Strength in the Orion A Filament

“…The POL-2 observations used in this analysis were originally presented by Ward-Thompson et al (2017), and form part of the JCMT BISTRO Large Program. We refer readers to that work for a detailed description of the data reduction, and summarize the key points here.…”

“…Faint 'striations' are seen in the low-density molecular gas parallel to the magnetic field direction, suggesting that material is accreting onto filaments along magnetic field lines (Sugitani et al 2011;Palmeirim et al 2013;Matthews et al 2014). Observations of high-mass star-forming regions have shown behaviour qualitatively similar to that in low-mass starforming regions (Ward-Thompson et al 2017). However, in order to accurately constrain the role of magnetic fields in high-mass filaments, and to understand the connection between the roles of magnetic fields in low-and high-mass star formation, detailed studies of the strength of magnetic fields in high-mass filaments, and their contribution to the energy balance of high-mass star-forming regions, must be undertaken.…”

“…The magnetic field of the OMC 1 region has an hourglass morphology (Schleuning 1998;Houde et al 2004;Ward-Thompson et al 2017). A variety of magnetic field strengths have been reported in OMC 1, ranging from a few hundred µG (Crutcher et al 1999, CN Zeeman effect, 23 ′′ resolution; Houde et al 2009, dust polarization, 12 ′′ resolution) to a few mG (Hansen & Johnston 1983, Norris 1984, Johnston et al 1989, Cohen et al 2006 ′′ resolution; Hildebrand et al 2009, dust polarisation, 20 ′′ resolution; Tang et al 2010, energetics arguments from 1 ′′ -resolution dust continuum observations).…”

“…The POL-2 data used in this work were taken as part of the BISTRO (B-Fields in Star-Forming Region Observations) survey (Ward-Thompson et al 2017) and as part of the POL-2 commissioning project. The BISTRO survey is observing the high-column-density regions of the molecular clouds of the Gould Belt (Herschel 1847;Gould 1879) in polarized light, in order to produce a large and homogeneous data set for the investigation of the role of magnetic fields in the physics of star formation in nearby molecular clouds.…”