Diffuse Hot Plasma in the Interstellar Medium and Galactic Outflows

TL;DR

This paper reviews the different phases of the interstellar medium in galaxies, focusing on hot plasma in various structures and its role in galactic outflows and feedback processes.

Contribution

It provides a comprehensive summary of observations and current understanding of hot plasma in the interstellar medium and galactic outflows.

Findings

Hot plasma exists in stellar bubbles, superbubbles, and outflows.

Galactic nuclear regions show enhanced star formation and cosmic ray acceleration.

Hot plasma is often dynamically unstable and over-pressurised.

Abstract

We summarise observations and our current understanding of the interstellar medium (ISM) in galaxies, which mainly consists of three phases: cold atomic or molecular gas and clouds, warm neutral or ionised gas, and hot ionised gas. These three gas phases form thermally stable states, while disturbances are caused by gravitation and stellar feedback in form of photons and shocks in stellar winds and supernovae. Hot plasma is mainly found in stellar bubbles, superbubbles, and Galactic outflows/fountains and is often dynamically unstable and is over-pressurised. In addition, in galactic nuclear regions, accretion onto the supermassive black hole causes enhanced star formation, outflows, additional heating, and acceleration of cosmic rays.