Supervirial 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 sight lines 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 kT = 0.176 ± 0.008 keV and the other at temperatures in the range kT = 0.65-0.90 keV. The uniform lower-temperature component is consistent with the Galaxy's virial temperature (∼10⁶ K). The temperatures of the hotter components are similar to that recently discovered (∼10⁷ K) in the sight line to blazar 1ES 1553+113, passing close to the Fermi bubble. Alternatively, the spectra can be described by just one lower-temperature component with supersolar neon abundance, once again similar to that found in the 1ES 1553+113 sight line. 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 supervirial 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.