Using Herschel and Planck observations to delineate the role of magnetic fields in molecular cloud structure

Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: soler@mpia.de

Received: 26 April 2019
Accepted: 7 August 2019

Abstract

We present a study of the relative orientation between the magnetic field projected onto the plane of sky (B_⊥) on scales down to 0.4 pc, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the distribution of gas column density (N_H) structures on scales down to 0.026 pc, derived from the observations by Herschel in submillimeter wavelengths, toward ten nearby (d < 450 pc) molecular clouds. Using the histogram of relative orientation technique in combination with tools from circular statistics, we found that the mean relative orientation between N_H and B_⊥ toward these regions increases progressively from 0°, where the N_H structures lie mostly parallel to B_⊥, with increasing N_H, in many cases reaching 90°, where the N_H structures lie mostly perpendicular to B_⊥. We also compared the relative orientation between N_H and B_⊥ and the distribution of N_H, which is characterized by the slope of the tail of the N_H probability density functions (PDFs). We found that the slopes of the N_H PDF tail are steepest in regions where N_H and B_⊥ are close to perpendicular. This coupling between the N_H distribution and the magnetic field suggests that the magnetic fields play a significant role in structuring the interstellar medium in and around molecular clouds. However, we found no evident correlation between the star formation rates, estimated from the counts of young stellar objects, and the relative orientation between N_H and B_⊥ in these regions.