On the formation of density filaments in the turbulent interstellar medium

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.