Self-ionizing galactic winds

Abstract

We present hydrodynamical simulations of galactic winds from star-forming galaxies including nonequilibrium 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 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.

Galactic Winds and Bubbles from Nuclear Starburst Rings

“…For models with lower thermalization efficiency and higher mass loading, the outflows will have lower velocities for which gravity may become important. We have further used a simple approximation radiative cooling and have neglected nonequilibrium ionization and irradiation effects, which is important to the ionization state of the outflow (Gray et al 2019;Sarkar et al 2022 . The X-ray surface brightness projected along the ŷ-direction, which represents an ideal edge-on view of the ring system at 20 Myr for simulations "A" and "A å " (from Figures 2 and 4).…”

Galactic winds and bubbles from nuclear starburst rings

“…For models with lower thermalization efficiency and higher mass-loading, the outflows will have lower velocities for which gravity may become important. We have further used a simple approximation radiative cooling, and have neglected non-equilibrium ionization and irradiation effects, which is important to the ionization state of the outflow (Gray et al 2019;Sarkar et al 2022).…”

Radiative turbulent mixing layers at high Mach numbers

“…In reality, supersonic flows are ubiquitous in observations and recent hydrodynamic simulations, say, associated with galactic outflows (e.g. Veilleux et al 1999;Li et al 2015;Li & Tonnesen 2020;Fielding & Bryan 2022;Girichidis et al 2021;Hopkins et al 2021;Sarkar et al 2022) and virial shocks in the CGM (e.g. Birnboim & Dekel 2003;Kereš et al 2005;Dekel & Birnboim 2006;Oppenheimer et al 2010;Faucher-Giguère et al 2011;Stern et al 2021;Ji et al 2021).…”