Molecular cloud formation in high-shear, magnetized colliding flows

TL;DR

This study uses magnetized colliding flow simulations with oblique shocks to show how shear and magnetic fields influence molecular cloud formation and star formation processes.

Contribution

It introduces the effects of oblique shocks and magnetic fields on cloud formation, highlighting how shear delays star formation and magnetic fields inhibit collapse.

Findings

Increased shear lengthens star formation timescales.

Magnetic fields prevent gravitational collapse in forming clouds.

Oblique shock interfaces tend to reorient to normal over time.

Abstract

The colliding flows (CF) model is a well-supported mechanism for generating molecular clouds. However, to-date most CF simulations have focused on the formation of clouds in the normal-shock layer between head-on colliding flows. We performed simulations of magnetized colliding flows that instead meet at an oblique-shock layer. Oblique shocks generate shear in the post-shock environment, and this shear creates inhospitable environments for star formation. As the degree of shear increases (i.e. the obliquity of the shock increases), we find that it takes longer for sink particles to form, they form in lower numbers, and they tend to be less massive. With regard to magnetic fields, we find that even a weak field stalls gravitational collapse within forming clouds. Additionally, an initially oblique collision interface tends to reorient over time in the presence of a magnetic field, so that it becomes normal to the oncoming flows. This was demonstrated by our most oblique shock interface, which became fully normal by the end of the simulation.