Statistical Assessment of Shapes and Magnetic Field Orientations in Molecular Clouds through Polarization Observations

TL;DR

This study uses polarization data from 24 molecular clouds to statistically infer that these clouds are mostly oblate disks with magnetic fields aligned near their shortest axes, despite limited sample size.

Contribution

It introduces a novel statistical method combining polarization observations and projection effects to determine intrinsic cloud shapes and magnetic field orientations.

Findings

Clouds are predominantly oblate disks.

Magnetic fields are aligned close to the shortest cloud axis.

Limited sample size restricts definitive conclusions.

Abstract

We present a novel statistical analysis aimed at deriving the intrinsic shapes and magnetic field orientations of molecular clouds using dust emission and polarization observations by the Hertz polarimeter. Our observables are the aspect ratio of the projected plane-of-the-sky cloud image, and the angle between the mean direction of the plane-of-the-sky component of the magnetic field and the short axis of the cloud image. To overcome projection effects due to the unknown orientation of the line-of-sight, we combine observations from 24 clouds, assuming that line-of-sight orientations are random and all are equally probable. Through a weighted least-squares analysis, we find that the best-fit intrinsic cloud shape describing our sample is an oblate disk with only small degrees of triaxiality. The best-fit intrinsic magnetic field orientation is close to the direction of the shortest cloud axis, with small (~24 deg) deviations toward the long/middle cloud axes. However, due to the small number of observed clouds, the power of our analysis to reject alternative configurations is limited.