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

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 $>4σ$, 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.