On the origin of the $10^7$ K hot emitting gas in the Circumgalactic medium of the Milky Way

TL;DR

This paper investigates the origin of the hot $10^7$ K gas in the Milky Way's circumgalactic medium, revealing it likely results from stellar feedback and is not in hydrostatic equilibrium, with implications for galaxy evolution.

Contribution

The study demonstrates that super-virial temperature gas is produced by stellar feedback and occupies extraplanar regions, providing new insights into the gas dynamics around the Milky Way.

Findings

Hot gas at $10^7$ K is produced by stellar feedback.

The gas is metal enriched and not in hydrostatic equilibrium.

Both virial and super-virial gases occupy disk-like extraplanar regions.

Abstract

The presence of the $\approx 10^6$ K gas in the circumgalactic medium of the Milky Way has been well established. However, the location and the origin of the newly discovered hot gas at `super-virial' temperatures of $\approx 10^7$ K have been puzzling. This hot gas has been detected in both absorption and emission; here we focus on the emitting gas only. We show that both the `virial' and the `super-virial' temperature gas as observed in \emph{emission} occupy disk-like extraplanar regions, in addition to the diffuse virial temperature gas filling the halo of the Milky Way. We perform idealized hydrodynamical simulations to show that the $\approx 10^7$ K emitting gas is likely to be produced by stellar feedback in and around the Galactic disk. We further show that the emitting gas at both super-virial and virial temperatures in the extraplanar regions is metal enriched and is not in hydrostatic equilibrium with the halo but is continuously evolving.