On the formation of density filaments in the turbulent interstellar medium

TL;DR

This paper explains the formation and properties of density filaments in the turbulent interstellar medium using MHD turbulence theory, highlighting the roles of turbulence, magnetic fields, and shock compression.

Contribution

It provides a theoretical framework linking interstellar turbulence characteristics to filament formation and alignment, incorporating neutral-ion decoupling and shock effects.

Findings

Perpendicular turbulent mixing leads to filament formation in diffuse media and molecular clouds.

Filament widths are determined by neutral-ion decoupling scales and turbulence properties.

Filament alignment with magnetic fields varies with turbulence conditions.

Abstract

This study is motivated by recent observations on the ubiquitous interstellar density filaments and guided by the modern theory of magnetohydrodynamic (MHD) turbulence. The interstellar turbulence shapes the observed density structure. The perpendicular turbulent mixing, as the fundamental dynamics of MHD turbulence, naturally entails parallel filaments presented in both the diffuse medium and molecular clouds (MCs). The minimum width is determined by the perpendicular neutral-ion decoupling scale in partially ionized media. Differently, dense perpendicular filaments arise in highly supersonic turbulence in MCs as a result of shock compression. Their width specifically depends on the turbulence properties. We demonstrate that different alignments of filaments with respect to the magnetic field originate from the varying turbulence properties in the multi-phase interstellar medium.