An Imprint of Molecular Cloud Magnetization in the Morphology of the Dust Polarized Emission

TL;DR

This paper introduces the Histogram of Relative Orientations (HRO) technique to analyze the magnetic field's influence on the morphology of density structures in simulated turbulent molecular clouds, revealing how magnetization affects their relative orientation.

Contribution

The study presents a new method, HRO, for characterizing the magnetic field's impact on molecular cloud structure and demonstrates its effectiveness across different magnetization levels in simulations.

Findings

Magnetic fields tend to align parallel to density structures in the simulations.

A transition from parallel to perpendicular orientation occurs at a critical density in highly magnetized clouds.

The change in orientation is more pronounced with stronger magnetic fields.

Abstract

We describe a morphological imprint of magnetization found when considering the relative orientation of the magnetic field direction with respect to the density structures in simulated turbulent molecular clouds. This imprint was found using the Histogram of Relative Orientations (HRO): a new technique that utilizes the gradient to characterize the directionality of density and column density structures on multiple scales. We present results of the HRO analysis in three models of molecular clouds in which the initial magnetic field strength is varied, but an identical initial turbulent velocity field is introduced, which subsequently decays. The HRO analysis was applied to the simulated data cubes and mock-observations of the simulations produced by integrating the data cube along particular lines of sight. In the 3D analysis we describe the relative orientation of the magnetic field $\mathbf{B}$ with respect to the density structures, showing that: 1.The magnetic field shows a preferential orientation parallel to most of the density structures in the three simulated cubes. 2.The relative orientation changes from parallel to perpendicular in regions with density over a critical density $n_{T}$ in the highest magnetization case. 3.The change of relative orientation is largest for the highest magnetization and decreases in lower magnetization cases. This change in the relative orientation is also present in the projected maps. In conjunction with simulations HROs can be used to establish a link between the observed morphology in polarization maps and the physics included in simulations of molecular clouds.