A disk-dominated and clumpy circumgalactic medium of the Milky Way seen in X-ray emission

TL;DR

This study reveals that the Milky Way's circumgalactic medium is primarily composed of a disk-like, clumpy hot plasma driven by stellar feedback, with indications of an extended halo component.

Contribution

It provides the first detailed survey of the Milky Way's CGM in soft X-ray emission, highlighting its disk-like structure and clumpiness, and suggests the presence of an extended halo.

Findings

X-ray emission is best modeled by a disk-like structure.

The CGM exhibits significant clumpiness on 10-degree scales.

An extended halo component is likely necessary to explain the observations.

Abstract

The Milky Way galaxy is surrounded by a circumgalactic medium (CGM) that may play a key role in galaxy evolution as the source of gas for star formation and a repository of metals and energy produced by star formation and nuclear activity. The CGM may also be a repository for baryons seen in the early universe, but undetected locally. The CGM has an ionized component at temperatures near $2 \times 10^{6}$~K studied primarily in the soft X-ray band. Here we report a survey of the southern Galactic sky with a soft X-ray spectrometer optimized to study diffuse soft X-ray emission. The X-ray emission is best fit with a disc-like model based on the radial profile of the surface density of molecular hydrogen, a tracer of star formation, suggesting that the X-ray emission is predominantly from hot plasma produced via stellar feedback. Strong variations in the X-ray emission on angular scales of $\sim10^{\circ}$ indicate that the CGM is clumpy. Addition of an extended, and possibly massive, halo component is needed to match the halo density inferred from other observations.