On the Origin of the 10 7 K Hot Emitting Gas in the Circumgalactic Medium of the Milky Way

Abstract

The presence of the ≈10 6 K gas in the circumgalactic medium of the Milky Way (MW) has been well established. However, the location and the origin of the newly discovered hot gas at “supervirial (SV)” temperatures of ≈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 SV temperature gas, as observed in emission, occupy disk-like extraplanar regions, in addition to the diffuse virial temperature gas filling the halo of the MW. We perform idealized hydrodynamical simulations to show that the ≈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 SV and virial temperatures in the extraplanar regions is metal enriched and is not in hydrostatic equilibrium with the halo but is continuously evolving.