The Milky Way's Kiloparsec Scale Wind: A Hybrid Cosmic-Ray and Thermally Driven Outflow

TL;DR

This paper models the Milky Way's kiloparsec-scale wind driven by cosmic rays and thermal gas, showing cosmic rays are crucial for wind acceleration and explaining observed X-ray and gamma-ray emissions.

Contribution

It introduces a hybrid cosmic-ray and thermal-driven wind model for the Milky Way, highlighting the role of cosmic rays in wind dynamics and emission profiles.

Findings

Cosmic-ray pressure is essential for driving the Galactic wind.

The wind model better explains diffuse soft X-ray emission than static models.

Cosmic rays influence the wind's properties and gamma-ray emission gradient.

Abstract

We apply a wind model, driven by combined cosmic-ray and thermal-gas pressure, to the Milky Way, and show that the observed Galactic diffuse soft X-ray emission can be better explained by a wind than by previous static gas models. We find that cosmic-ray pressure is essential to driving the observed wind. Having thus defined a "best-fit" model for a Galactic wind, we explore variations in the base parameters and show how the wind's properties vary with changes in gas pressure, cosmic-ray pressure and density. We demonstrate the importance of cosmic rays in launching winds, and the effect cosmic rays have on wind dynamics. In addition, this model adds support to the hypothesis of Breitschwerdt and collaborators that such a wind may help explain the relatively small gradient observed in gamma-ray emission as a function of galactocentric radius.