Self-ionizing galactic winds

TL;DR

This paper presents advanced hydrodynamical simulations of galactic winds incorporating non-equilibrium ionization and frequency-dependent radiative transfer, revealing significant impacts on ionization states and observable spectra, crucial for accurate modeling.

Contribution

It introduces the first detailed simulations of galactic winds including non-equilibrium ionization and self-radiation effects, improving interpretation of observational data.

Findings

Non-equilibrium ionization leads to over-ionized gas and higher ion column densities.

Wind radiation significantly enhances soft X-ray emission compared to background.

Equilibrium models may overestimate temperature and density by up to two orders of magnitude.

Abstract

We present hydrodynamical simulations of galactic winds from star-forming galaxies including non-equilibrium ionization and frequency-dependent radiative transfer, processes that have remained largely unaccounted for in galactic wind studies. We consider radiation from massive stars, the metagalactic UV/X-ray background, and the self-radiation of the supernovae heated gas. We compare our results to classical galactic wind solutions and show the importance of our newly included physical processes toward observations of ions such as O III, O VI, O VII and O VIII plus the observable soft X-ray spectra. Non-equilibrium ionization is reflected in over-ionized gas compared to equilibrium solutions, leading to much enhanced column densities of highly ionized species. The wind produces excess soft X-ray ($E\gtrsim 100$ eV) radiation that is several orders of magnitude higher compared to the metagalactic background. This radiation ionizes the higher ions (such as O VII) somewhat, but affects the lower ions (such as O III) significantly. We predict that the observable X-ray spectra should contain the signatures of such non-equilibrium effects, especially in X-ray lines such as O VII and O VIII. Simple estimates suggest that both the temperature and density of the winds may be overestimated by factors of a few to almost 2 orders of magnitude using simple equilibrium models. We conclude that both the non-equilibrium ionization and the radiation from the wind itself need to be considered for proper modeling of the optical/UV/X-ray emitting plasma in galactic winds.