Super-virial temperature or Neon overabundance?: Suzaku observations of the Milky Way circumgalactic Medium

TL;DR

This study uses Suzaku and Chandra data to analyze the Milky Way's circumgalactic medium, revealing either super-virial temperature gas or Neon overabundance, with implications for understanding the CGM's properties.

Contribution

It provides the first detailed characterization of the CGM's thermal components and Neon abundance, highlighting the widespread presence of hot gas or Neon overabundance.

Findings

Two thermal components identified in the CGM, at 0.176 keV and 0.65-0.90 keV.

Super-virial temperature gas or Neon overabundance is required at >4σ significance.

Hot gas or Neon overabundance is widespread and not solely related to the Fermi bubble.

Abstract

We analyzed Suzaku and Chandra observations of the soft diffuse X-ray background toward four sightlines with the goal of characterizing the X-ray emission from the Milky Way circumgalactic medium (CGM). We identified two thermal components of the CGM, one at a uniform temperature of $\rm kT = 0.176\pm0.008 ~keV$ and the other at temperatures ranging between $\rm kT = 0.65-0.90~ keV$. The uniform lower temperature component is consistent with the Galaxy's virial temperature ($ \sim10^{6}~ K$). The temperatures of the hotter components are similar to that recently discovered ($\rm \sim 10^{7}~ K$; Das et al.) in the sightline to blazar 1ES1553+113, passing close to the Fermi bubble. Alternatively, the spectra can be described by just one lower-temperature component with super-solar Neon abundance, once again similar to that found in the 1ES1553+113 sightline. The additional hot component or the overabundance of Ne is required at a significance of $>4\sigma$, but we cannot distinguish between the two possibilities. These results show that the super-virial temperature gas or an enhanced Ne abundance in the warm-hot gas in the CGM is widespread, and these are not necessarily related to the Fermi bubble.