A Model for Line Absorption and Emission from Turbulent Mixing Layers

TL;DR

This paper develops a 1D model for turbulent mixing layers that accurately predicts observable properties like column densities and line ratios, aligning well with observations and enabling improved large-scale simulations.

Contribution

It introduces a simple 1D conductive-cooling front model that reproduces 3D simulation results for TMLs, facilitating sub-grid predictions in large-scale models.

Findings

The model accurately predicts column densities and line ratios.

Predicted line ratios match observations well.

Multiple mixing layers are needed to explain observed column densities.

Abstract

Turbulent mixing layers (TMLs) are ubiquitous in multiphase gas. They can potentially explain observations of high ions such as O VI, which have significant observed column densities despite short cooling times. Previously, we showed that global mass, momentum and energy transfer between phases mediated by TMLs is not sensitive to details of thermal conduction or numerical resolution. By contrast, we show here that observables such as temperature distributions, column densities and line ratios are sensitive to such considerations. We explain the reason for this difference. We develop a prescription for applying a simple 1D conductive-cooling front model which quantitatively reproduces 3D hydrodynamic simulation results for column densities and line ratios, even when the TML has a complex fractal structure. This enables sub-grid absorption and emission line predictions in large scale simulations. The predicted line ratios are in good agreement with observations, while observed column densities require numerous mixing layers to be pierced along a line of sight.