Modeling Dust Polarization Observations of Molecular Clouds through MHD Simulations

TL;DR

This study compares observed dust polarization in a molecular cloud with MHD simulations to understand magnetic field orientation and turbulence effects, revealing that observed polarization properties depend heavily on magnetic field inclination and turbulence.

Contribution

It introduces a comparison framework between BLASTPol observations and synthetic MHD simulations assuming homogeneous grain alignment, highlighting the impact of magnetic field orientation.

Findings

Magnetic field orientation significantly influences polarization distributions.

Observed polarization suggests either a line-of-sight magnetic field or strong turbulence.

Simple grain alignment models do not fully explain polarization-column density correlations.

Abstract

The BLASTPol observations of Vela C have provided the most detailed characterization of the polarization fraction $p$ and dispersion in polarization angles $S$ for a molecular cloud. We compare the observed distributions of $p$ and $S$ with those obtained in synthetic observations of simulations of molecular clouds, assuming homogeneous grain alignment. We find that the orientation of the mean magnetic field relative to the observer has a significant effect on the $p$ and $S$ distributions. These distributions for Vela C are most consistent with synthetic observations where the mean magnetic field is close to the line-of-sight. Our results point to apparent magnetic disorder in the Vela C molecular cloud, although it can be due to either an inclination effect (i.e., observing close to the mean field direction) or significant field tangling from strong turbulence/low magnetization. The joint correlations of $p$ with column density and of $S$ with column density for the synthetic observations generally agree poorly with the Vela C joint correlations, suggesting that understanding these correlations require a more sophisticated treatment of grain alignment physics.