Estimation of the magnetic field strength from ALMA dust polarization in the protocluster G327.29

Abstract

Magnetic fields and turbulence may play a crucial role in the evolution of molecular clouds and ultimately in the formation of dense cores and stars. Despite being studied in many molecular clouds, the exact role of magnetic fields and turbulence in star formation is still poorly understood. Here, we report the high resolution plane of sky magnetic field (B_pos) morphology toward the high mass star forming region G327.29, obtained with the 12-meter of the Atacama Large Millimeter/sub-millimeter Array (ALMA) telescope. From our analysis, we obtain a complex B_pos morphology where the magnetic field orientation is uniformly distributed across the entire range from -90 to +90 deg. The observed area is composed of one filament and one dense central clump, which harbor multiple dense cores. The total magnetic field strengths (B_tot) in these regions are 1.4 \pm 0.7 mG and 2.0 \pm 0.8 mG at a number density (n) of 6.8 \pm 1.5 x 10^5 and 1.1 \pm 0.3 x 10^6 cm^-3 , derived from the angular dispersion function (ADF) method. The virial parameters (α vir )in these regions are 7.7 \pm 7.1 and 0.7 \pm 0.6, suggesting that the regions may be gravitationally bound or unbound after accounting for the errors. Moreover, the ratio of turbulent to magnetic energy (~ 0.25) indicates that the magnetic field is dynamically more important than turbulence. The relative influence of turbulence and magnetic fields on core dynamics appears to depend on how the B_tot scales with gas density (\r{ho}) in the densest regions. In summary, this work presents a comprehensive analysis of the relative roles of magnetic fields, turbulence, and gravity in regulating high-mass star formation in G327.29, enabled by high-resolution ALMA observations.

Figures (23)

• Figure 1: Left: The color image presents the Spitzer (GLIMPSE) 8 $\mu$m emission toward the G327.29 star-forming region 2003PASP..115..953B. The contours represent the ATLASGAL 870 $\mu$m emission obtained from 2009AA...504..415S. Contour levels range from 0.45 to 34 Jy beam$^{-1}$ respectively with a 19.2$"$ beam. Middle: Map of the 1.2 mm continuum emission toward the central clump (protocluster) from the ALMA-IMF large program 2022AA...662A...8M. The two blue dashed circles mark the areas observed for polarization with the ALMA 12m array. Right: 1.2 mm continuum emission map obtained in this work by mosaicking the two pointings shown in the middle panel.
• Figure 2: Dust temperature ($T_{\text{d}}$) map in the G327.29 region obtained from the work of 2024AA...687A.217D. We masked the regions where no 1.2 mm continuum emission was observed in our analysis. Region 1 and Region 2 are two distinct areas where we estimate the magnetic field separately.
• Figure 3: Distribution of the number of components of the HN$^{13}$C (J=3$-$2) and H$^{13}$CO$^{+}$ (J=3$-$2) lines.
• Figure 4: Velocity dispersion ($\sigma_{\text{tot}}$) maps of HN$^{13}$C (3$-$2) and H$^{13}$CO$^{+}$ (3$-$2) lines obtained from the pixel-wise fitting using Gausspy+ module. Region 1 and Region 2 are analyzed independently to estimate the magnetic field.
• Figure 5: Upper Left: Observed filament in the Region 1. The black solid line is the ridgeline of the filament. Upper Right: Same filament after straightening the ridgeline vertically. Due to certain jumps in the middle of the ridge line, those rows were masked. Here the length of the filament is denoted by symbol L which is equal to $\sim$ 0.20 pc. Lower: Radial profile of the integrated intensity (I) of the filament. Here the solid lightskyblue and red lines are the mean and dispersion ($\sigma$) values at each concentric cylindrical shell. We set the radius (R) at $\sim$ 0.03 pc, because beyond that I decreases sharply and returns to flat. This is indicated by the blue dashed vertical line. This phenomenon is caused because of the mass distribution not being symmetrical on both sides of the ridgeline of the filament.