Theory and Models of the Disc-Halo Connection

TL;DR

This paper reviews the disc-halo connection in star-forming galaxies, using analytical and simulation methods to explore how star formation rates influence galactic fountains and winds, affecting galaxy evolution and observable X-ray spectra.

Contribution

It introduces a comprehensive model linking star formation, galactic winds, and X-ray spectral signatures, validated through simulations and application to NGC 3079.

Findings

Galactic fountains depend on star formation rates.

High star formation and cosmic ray coupling produce galactic winds.

Synthetic spectra can successfully fit observed X-ray spectra.

Abstract

We review the evolution of the interstellar medium in disc galaxies, and show, both analytically and by numerical 3D hydrodynamic simulations, that the disc-halo connection is an essential ingredient in understanding the evolution of star forming galaxies. Depending on the star formation rate of the underlying gaseous disc, a galactic fountain is established. If the star formation rate is sufficiently high and/or cosmic rays are well coupled to the thermal plasma, a galactic wind will be formed and lead to a secular mass loss of the galaxy. Such a wind leaves a unique imprint on the soft X-ray spectra in edge-on galaxies, with delayed recombination being one of its distinctive features. We argue that synthetic spectra, obtained from self-consistent dynamical and thermal modelling of a galactic outflow, should be treated on an equal footing as observed spectra. We show that it is thus possible to successfully fit the spectrum of the starburst galaxy NGC 3079.