Structure of dynamical condensation fronts in the interstellar medium

TL;DR

This paper explores the detailed structure of condensation fronts in the interstellar medium, revealing a wider parameter range for phase coexistence and highlighting how heat conduction's role diminishes with increased mass flux.

Contribution

It provides new solutions for condensation front structures across broader pressure and mass flux ranges, including shock-compressed regions relevant to molecular cloud formation.

Findings

Wider pressure range for phase coexistence in condensation fronts.

Transition layer thickness characterized by cooling length at high mass flux.

Heat conduction becomes less significant with increasing mass flux.

Abstract

In this paper, we investigate the structure of condensation fronts from warm diffuse gas to cold neutral medium (CNM) under the plane parallel geometry. The solutions have two parameters, the pressure of the CNM and the mass flux across the transition front, and their ranges are much wider than previously thought. First, we consider the pressure range where the three phases, the CNM, the unstable phase, and the warm neutral medium, can coexist in the pressure equilibrium. In a wide range of the mass flux, we find solutions connecting the CNM and the unstable phase. Moreover, we find solutions in larger pressure range where there is only one thermal equilibrium state or the CNM. These solutions can be realized in shock-compressed regions that are promising sites of molecular cloud formation. We also find remarkable properties in our solutions. Heat conduction becomes less important with increasing mass flux, and the thickness of the transition layer is characterized by the cooling length instead of the Field length.