The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65$^\circ $$\lt$$\ell$$\lt$ 295$^\circ $ to avoid contributions from the very bright diffuse source that extends at least 30$^\circ $ from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17 $\times$ 10$^{-6}$cs$^{-1}$arcmin$^{-2}$ in R45-band. The OVII and OVIII intensities are well correlated to each other, and OVII emission shows an intensity floor at $\sim$2 photonss$^{-1}$cm$^{-2}$str$^{-1}$ (LU). The high-latitude OVIII emission shows a tight correlation with excess of OVII emission above the floor, with (OVIII intensity) $=$ 0.5 $\times$ [(OVII intensity) $-$ 2LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around $\sim$0.2 keV. We consider that the offset intensity of OVII arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess OVII (2–7LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 $\times$ 10$^{39}$ergs$^{-1}$, and its characteristic temperature may be related to the virial temperature of the Galaxy.
We present a detailed spectroscopic study of the hot gas in the Galactic halo toward the direction of a blazer PKS 2155$-$304 ($z =$ 0.117). The O VII and O VIII absorption lines were measured with the Low and High Energy Transmission Grating Spectrographs aboard Chandra, and the O VII, O VIII, and Ne IX emission lines produced in an adjacent field of the PKS 2155$-$304 direction were observed with the X-ray Imaging Spectrometer aboard Suzaku. Assuming vertically exponential distributions of the gas temperature and the density, we performed a combined analysis of the absorption and emission data. The gas temperature and the density at the galactic plane were determined to be (2.5$^{+0.6}_{-0.3}$) $\times$ 10$^{6} $K and ($1.4^{+0.5}_{-0.4}$) $\times$ 10$^{-3} $cm$^{-3} $, and the scale heights of the gas temperature and density were 5.6$^{+7.4}_{-4.2}$ kpc and 2.3$^{+0.9}_{-0.8}$ kpc, respectively. These values are consistent with those obtained in the LMC X-3 direction.
Although about 40% of the soft X-ray background emission in 0.4 to 1 keV range has extragalactic origins and thus is totally blocked by the galactic absorption in midplane directions, it decreases at most by about 20% in midplane. Suzaku observation of the direction, ($\ell$, $b$) $=$ (235$^\circ$, 0$^\circ$), showed an O vii${\rm K} \alpha$ emission intensity comparable with that of the MBM-12 on cloud Suzaku observation, but revealed a narrow bump peaked at $\sim$0.9 keV. The latter component is partly filling the decrease of the extragalactic component in midplane. The feature can be well represented by a thin thermal emission with a temperature of about 0.8 keV. Because of the high pressure implied for spatially extended hot gas, the emission is likely a sum of unresolved faint sources. We consider a large fraction of the emission originates from faint dM stars. We constructed a model spectrum for spatially unresolved dM stars that consistently explains the observed spectrum and the surface brightness. The model also suggests that the emission from dM stars decreases very rapidly with increasing $b$, and thus that it cannot compensate entirely the decrease of the extragalactic component at $b$$\sim$ 2$^\circ$–10$^\circ$.
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