Catastrophic Cooling in Superwinds. III. Non-equilibrium Photoionization

TL;DR

This paper models starburst-driven superwinds with non-equilibrium radiative cooling and photoionization, revealing enhanced UV line emissions and improving understanding of feedback processes in star-forming galaxies.

Contribution

It introduces a combined simulation approach using MAIHEM, FLASH, and CLOUDY to study non-equilibrium cooling and photoionization in superwinds, a novel integration for this context.

Findings

Enhanced C IV emission in metal-rich superwinds.

Increased O VI emission in metal-poor superwinds.

Non-equilibrium models better reproduce observed line emissions.

Abstract

Observations of some starburst-driven galactic superwinds suggest that strong radiative cooling could play a key role in the nature of feedback and the formation of stars and molecular gas in star-forming galaxies. These catastrophically cooling superwinds are not adequately described by adiabatic fluid models, but they can be reproduced by incorporating non-equilibrium radiative cooling functions into the fluid model. In this work, we have employed the atomic and cooling module MAIHEM implemented in the framework of the FLASH hydrodynamics code to simulate the formation of radiatively cooling superwinds as well as their corresponding non-equilibrium ionization (NEI) states for various outflow parameters, gas metallicities, and ambient densities. We employ the photoionization program CLOUDY to predict radiation- and density-bounded photoionization for these radiatively cooling superwinds, and we predict UV and optical line emission. Our non-equilibrium photoionization models built with the NEI states demonstrate the enhancement of C IV, especially in metal-rich, catastrophically cooling outflows, and O VI in metal-poor ones.