Energy spectra of the soft x-ray diffuse emission in fourteen fields observed with Suzaku

Abstract

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° < ℓ < 295° to avoid contributions from the very bright diffuse source that extends at least 30° 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 × 10-6c s-1 arcmin-2 in R45-band. The O VII and O VIII intensities are well correlated to each other, and O VII emission shows an intensity floor at ∼ 2 photons s-1cm -2str-1 (LU). The high-latitude O VIII emission shows a tight correlation with excess of O VII emission above the floor, with (O VIII intensity) = 0.5 × [(O VII intensity) - 2 LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around ∼ 0.2 keV. We consider that the offset intensity of O VII arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess O VII (2-7 LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 × 1039ergs-1, and its characteristic temperature may be related to the virial temperature of the Galaxy. © 2009. Astronomical Society of Japan.