Magnetic fields in the close neighborhood of LDN 328 core

TL;DR

This study probes how magnetic fields influence the evolution and fragmentation of material around the LDN 328 core by combining JCMT/SCUBA-2/POL-2 850 μm polarization with Herschel SED-based dust temperatures and column densities. It uses FellWalker to identify 14 clumps, performs relative-orientation analyses between clump major axes and B-field, and applies the Davis-Chandrasekhar-Fermi framework, including a structure-function extension, to estimate plane-of-sky field strengths around $B_{ ext{pos}} ≈ 83$ μG in key regions. The results show sub-Alfvénic, magnetically influenced conditions with mass-to-flux ratios in the subcritical to transcritical range and depolarization trends with increasing density, indicating magnetic fields play a significant role in delaying collapse and guiding material flow. The work connects multi-scale magnetic-field structures from Planck-scale to sub-parsec scales and demonstrates how magnetic pressure and turbulence compete to shape early star formation in clustered environments, with implications for initial conditions in core formation.

Abstract

Linearly polarized dust emission traces the plane-of-sky magnetic field structure, thus allowing us to investigate the role of magnetic fields in the formation and evolution of cloud cores. In this work, we present observations of dust polarization at 850 $μ{\rm m}$ wavelength toward the LDN\,328 (hereafter, L328) core and its neighborhood regions, classified as R1, R2, and R3, using the James Clerk Maxwell Telescope (JCMT) with SCUBA-2/POL-2. This study extends our previous work on magnetic fields in L328 across different spatial scales. We used the JCMT/POL-2 data in the near vicinity of the L328 core to study the magnetic fields in its nearby regions. We identified clumps in these regions using the \texttt{FellWalker} algorithm and derived the dust temperature and column density by fitting the spectral energy distribution (SED) using combined JCMT and \textit{Herschel} dust continuum maps. We analyzed the magnetic field morphology in the vicinity of the L328 core and employed the structure function analysis to determine the magnetic field dispersion angle. We used the modified Davis-Chandrasekhar-Fermi (DCF) method to estimate magnetic field strengths and also derived the mass-to-flux ratio and Alfvén Mach number.

Figures (11)

• Figure 1: Left: DSS red continuum-subtracted H$\alpha$ image of the L328 and L331 regions. Right: 850 $\mu$m dust continuum map overlaid with B-field vectors obtained from SCUBA-2/POL-2, with the orange circle indicating the beam size. The dotted lines outline the zoomed region. Scale bars are shown in the bottom right of both panels. The yellow contour is at 35 Jy/beam, and the white contour is at 70 Jy/beam, taken from the 850 µm continuum image in both images.
• Figure 2: The central panel shows the SCUBA-2/POL-2 850 $\mu$m dust continuum map overlaid with B-field vectors, highlighting the regions R1, R2, R3, and the L328 core as introduced in the text. The surrounding panels show the individual zoomed-in images of these regions with B-field vectors overlaid. The scale bar is shown at the bottom left of each image.
• Figure 3: Clumps identified using the FellWalker algorithm are shown as ellipses overlaid on the 850 $\mu$m continuum image. The clump numbering follows a right-to-left order. Submillimeter sources are marked with ‘+’, and YSO sources are indicated with ‘*’.
• Figure 4: The left panel shows the fitted dust temperature $T_{\text{d}}$ map, and the right panel shows the corresponding column density $N({\text{H$_2$}}$) map. The overlaid ellipse on both plots are the clumps from the SCUBA-2 850 $\mu$m dust emission map. Each map is smoothed to the 352 beam size of the Herschel 500 $\mu$m observations, which is shown by the circle in the upper left corner.
• Figure 5: Left: 850 $\mu$m dust continuum map overplotted with B-field vectors from SCUBA-2/POL-2 (white) and optical observations (red), with the orange circle indicating the beam size. Right: The SCUBA-2/POL-2 850 $\mu$m dust continuum map is overplotted with color coded circles representing the relative angle between the clump’s major axis and the mean B-field orientation. The color scale spans from 0$^\circ$ (blue) to 180$^\circ$ (red). The orange circle at the bottom left indicates the beam size, and the scale bar at the bottom right.