Probing the magnetic fields and dust properties in the young embedded star-forming region AFGL 6366S using Near Infrared and Optical linear polarimetry

TL;DR

This study uses near-infrared and optical polarimetry to analyze magnetic fields, dust properties, and grain alignment in the young star-forming region AFGL 6366S, revealing complex magnetic structures and grain disruption effects.

Contribution

It provides detailed magnetic field morphology and dust grain analysis in AFGL 6366S, highlighting the role of radiative torque disruption and mass flows in star formation.

Findings

Magnetic field wraps around dense clumps with significant misalignment to Galactic field.

Detection of a polarization hole due to grain disruption and magnetic tangling.

Clumps exhibit different mass-to-flux ratios, indicating varied magnetic criticality.

Abstract

We present Near-Infrared (NIR) and Optical linear polarimetry towards the partially embedded cluster AFGL 6366S. The polarization ranges from 0.44-10.3 per cent in NIR and 0.16-11.22 per cent in Optical bands. The position angle spans $1^\circ - 179^\circ$ in both NIR and Optical bands. About 22 stars exhibit intrinsic polarization signatures. A polarization hole is evident towards the densest ($\sim 3.4 \times 10^{23} \mathrm{cm}^{-2}$) and warmest ($\sim 28.8 \mathrm{K}$) central cluster region. It is attributable to depolarization induced by Radiative Torque Disruption (RAT-D) of large grains and a modest contribution from magnetic-field tangling. The local magnetic field towards the cluster's central region is significantly misaligned with both the large-scale Galactic field and the long axis of the filament present in the region. The field morphology wraps around two dense molecular clumps of radii 0.34 pc and 0.22 pc and $\mathrm N(\mathrm H_2)$ = $(7.9 \pm 1.1) \times 10^{22}$ cm$^{-2}$ and $(4.3 \pm 0.5) \times 10^{22}$ cm$^{-2}$, respectively. The clumps are embedded in the filamentary structure and represent locally accelerated stages of mass accumulation. Gravitationally driven mass flows, largely perpendicular to the local magnetic field, produce a U-shaped field curvature across the filament axis. The plane-of-sky magnetic field strengths towards the two clumps are $ 447.91 \pm 83.81 \mu\mathrm{G}$ and $396.66 \pm 73.64 \mu\mathrm{G}$. The corresponding mass-to-flux ratios ($\lambda \sim 1.34$ and $0.82$) indicate that one clump is magnetically supercritical and the other is subcritical. The Alfven Mach numbers ($\mathcal{M}_A$) $\sim$ 0.395 and 0.393 indicate that both the clumps are in sub-Alfv\'enic state.