# Radiation hydrodynamics simulations of the evolution of the diffuse ionized gas in disc galaxies

## TL;DR

This study uses radiation hydrodynamics simulations to demonstrate that photoionization feedback can support the diffuse ionized gas layer in disc galaxies, explaining its pressure and turbulence.

## Contribution

It presents the first fully consistent radiation hydrodynamics model of the diffuse ionized gas in disc galaxies, highlighting the role of photoionization in gas support.

## Key findings

- Photoionization feedback drives turbulence in galactic discs.
- Pressure support for the DIG is provided by photoionization.
- A natural balance exists between ionizing radiation and gas phases.

## Abstract

There is strong evidence that the diffuse ionized gas (DIG) in disc galaxies is photoionized by radiation from UV luminous O and B stars in the galactic disc, both from observations and detailed numerical models. However, it is still not clear what mechanism is responsible for providing the necessary pressure support for a diffuse gas layer at kpc-scale above the disc. In this work we investigate if the pressure increase caused by photoionization can provide this support. We run self-consistent radiation hydrodynamics models of a gaseous disc in an external potential. We find that photoionization feedback can drive low levels of turbulence in the dense galactic disc, and that it provides pressure support for an extended diffuse gas layer. Our results show that there is a natural fine-tuning between the total ionizing radiation budget of the sources in the galaxy and the amount of gas in the different ionization phases of the ISM, and provide the first fully consistent radiation hydrodynamics model of the DIG.