Statistical analysis of the interplay between magnetic fields and filaments hosting Planck Galactic Cold Clumps

TL;DR

This study statistically examines how magnetic fields relate to interstellar filaments with cold clumps, revealing density-dependent orientation patterns and highlighting magnetic influence on filament formation and evolution.

Contribution

It introduces a comprehensive analysis considering environmental density and filament contrast, providing new insights into magnetic field and filament orientation relationships.

Findings

Low contrast filaments align parallel to magnetic fields in low-density environments.

High contrast filaments tend to have random orientations relative to magnetic fields.

A transition from parallel to perpendicular orientation occurs at a density of about 10^3 cm^-3.

Abstract

We present a statistical study of the relative orientation in the plane of the sky between interstellar magnetic fields and filaments hosting cold clumps. For the first time, we consider both the density of the environment and the density contrast between the filaments and their environment. Moreover, we geometrically distinguish between the clumps and the remaining portions of the filaments. We infer the magnetic field orientations in the filaments and in their environment from the Stokes parameters, assuming optically thin conditions. Thus, we analyze the relative orientations between filaments, embedded clumps, and internal and background magnetic fields, depending on the filament environment and evolutionary stages. We recover the previously observed trend for filaments in low column density environments to be aligned parallel to the background magnetic field; however, we find that this trend is significant only for low contrast filaments, whereas high contrast filaments tend to be randomly orientated with respect to the background magnetic field. Filaments in high column density environments do not globally show any preferential orientation, although low contrast filaments alone tend to have perpendicular relative orientation with respect to the background magnetic field. For a subsample of nearby filaments, for which volume densities can be derived, we find a clear transition in the relative orientation with increasing density, at $n_{\rm H} \sim 10^{3}~{\rm cm}^{-3}$, changing from mostly parallel to mostly perpendicular in the off-clump portions of filaments and from even to bimodal in the clumps. Our results confirm a strong interplay between interstellar magnetic fields and filaments during their formation and evolution.