Dust polarized emission observations of NGC 6334

Abstract

Context. Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained. Aims. We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation. Methods. We present new observations of the dust polarized emission at 850 μm toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with the James Clerk Maxwell Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (PI), the polarization fraction (PF), and the plane-of-the-sky B-field angle (χB_POS) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and χBPOS along the ridge crest and compared them with the results obtained from simulated filaments. Results. The observations span ~3 orders of magnitude in Stokes I and PI and ~2 orders of magnitude in PF (from ~0.2 to ~ 20%). A large scatter in PI and PF is observed for a given value of I. Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc), χBPOS varies coherently along the crests of the filament network. The observed power spectrum of χBPOS can be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that of I. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, χBPOS rotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in PF toward the high-column density (NH2 ≳ 1023 cm−2) star cluster-forming hubs. These latter large PF values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure. Conclusions. These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.

Magnetic Fields in Massive Star-Forming Regions (MagMaR) II. Tomography Through Dust and Molecular Line Polarization in NGC 6334I(N)

“…Recently, observations with the James Clerk Maxwell Telescope (JCMT) of polarized dust emission at 850 µm revealed a detailed field morphology of NGC6334I(N) at clump scales (14 resolution, Arzoumanian et al 2021). To compare with ours, we show a zoomed map of the JCMT data (see Figure 3, left panel), where the pinched morphology is seen over a broader region encompassing both NGC6334I(N) and NGC6334I sources (NGC6334I is not covered by the ALMA data presented here) and outlined by translucent red lines.…”

“…The brightest regions studied in the millimeter and sub-millimeter are NGC6334I and NGC6334I(N) (McCutcheon et al 2000;Hunter et al 2014Hunter et al , 2017Sadaghiani et al 2020), where both regions appear to harbor high mass star formation. Besides the large scale mapping of polarized dust emission done by Planck (Planck Collaboration XXXV et al 2016), the magnetic field in NGC6334I(N) has been mapped via polarized dust emission at angular resolutions from ∼ 4 (Li et al 2006), ∼ 20 Vaillancourt (2011, ∼ 14 (Arzoumanian et al 2021), and ∼ 2 (Zhang et al 2014;Li et al 2015) which found a field shape evolving from a clear pinch at the high density peaks at large scales to an "hourglass" shape at shorter scales. We follow the nomenclature used by Hull & Zhang (2019), where we refer to cloud scales to structures ∼ 10 pc, clump scales ∼ 1 pc, core scales between 0.1 to 0.01 pc, and envelope scales to structures ∼ 1000 au.…”

The JCMT BISTRO Survey: The Distribution of Magnetic Field Strengths toward the OMC-1 Region

“…The results of the BISTRO surveys have shown highly resolved magnetic fields and measurements of the field strengths in Orion A ), Oph-A (Kwon et al 2018), Oph-B (Soam et al 2018), Barnard 1 (Coudé et al 2019), Oph-C (Liu et al 2019), IC 5146 (Wang et al 2019), M16 (Pattle et al 2018), NGC 6334 (Arzoumanian et al 2021), and several other regions are under investigation.…”

A systematic bias in fitting the surface-density profiles of interstellar filaments

“…In the last decade it has become clear that filaments play a critical role in assembling the material to form stars (e.g. Schneider & Elmegreen 1979;Bally et al 1987;Abergel et al 1994;Cambrésy 1999;Myers 2009;Hacar & Tafalla 2011;Peretto et al 2012;Hacar et al 2013;Palmeirim et al 2013;André et al 2014;Alves de Oliveira et al 2014;Peretto et al 2013;Könyves et al 2015;Marsh et al 2016;Hacar et al 2017;Ward-Thompson et al 2017;Williams et al 2018;Hacar et al 2018;Watkins et al 2019;Ladjelate et al 2020;Arzoumanian et al 2021). Even in clouds that are not apparently forming stars, or forming them very slowly (e.g.…”