SCUPOL Magnetic Field Analysis

TL;DR

This study analyzes 850 micron polarization maps of molecular clouds and star-forming regions, comparing observations with 3D MHD simulations to understand magnetic field properties and turbulence.

Contribution

It demonstrates that simple ideal MHD simulations can effectively reproduce large-scale magnetic and turbulence properties of molecular cloud envelopes.

Findings

Simulations match observed turbulence regimes within a factor of 2.

Magnetic field inclination angles are constrained and consistent with other methods.

Turbulent Alfvèn and sonic Mach numbers are estimated accurately from data.

Abstract

We present an extensive analysis of the 850 microns polarization maps of the SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the molecular clouds and star-forming regions. For the sufficiently sampled regions, we characterize the depolarization properties and the turbulent-to-mean magnetic field ratio of each region. Similar sets of parameters are calculated from 2D synthetic maps of dust emission polarization produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and DR21 molecular clouds polarization maps. For these specific regions the turbulent MHD regimes retrieved from the simulations, as described by the turbulent Alfv\`en and sonic Mach numbers, are consistent within a factor 1 to 2 with the values of the same turbulent regimes estimated from the analysis of Zeeman measurements data provided by Crutcher (1999). Constraints on the values of the inclination angle of the mean magnetic field with respect to the LOS are also given. The values obtained from the comparison of the simulations with the SCUPOL data are consistent with the estimates made by use of two different observational methods provided by other authors. Our main conclusion is that simple ideal, isothermal and non-selfgraviting MHD simulations are sufficient to describe the large scale observed physical properties of the envelopes of this set of regions.