The stellar distribution derived from an H and K _ { \mathrm { S } } -band survey of the central region of our Galaxy is compared with the Fe \emissiontype XXV K \alpha ( 6.7 keV ) line intensity observed with the Suzaku satellite .
The survey is for the Galactic coordinates |l| \lesssim 3 \arcdeg . 0 and |b| \lesssim 1 \arcdeg . 0 ( equivalent to 0.8 kpc \times 0.3 kpc for R _ { 0 } = 8 kpc ) , and the number-density distribution N ( K _ { \mathrm { S } , 0 } ;l,b ) of stars is derived using the extinction-corrected magnitude K _ { \mathrm { S } , 0 } = 10.5 .
This is deep enough to probe the old red giant population and in turn to estimate the ( l , b ) distribution of faint X-ray point sources such as coronally active binaries and cataclysmic variables .
In the Galactic plane ( b = 0 \arcdeg ) , N ( 10.5 ;l,b ) increases to the Galactic center as |l| ^ { -0.30 \pm 0.03 } in the range of -0 \arcdeg . 1 \geq l \geq - 0 \arcdeg . 7 , but this increase is significantly slower than the increase ( |l| ^ { -0.44 \pm 0.02 } ) of the Fe \emissiontype XXV K \alpha line intensity .
If normalized with the ratios in the outer region 1 \arcdeg . 5 \leq|l| \leq 2 \arcdeg . 8 , where faint X-ray point sources are argued to dominate the diffuse Galactic X-ray ridge emission , the excess of the Fe \emissiontype XXV K \alpha line intensity over the stellar number density is at least a factor of two at |l| = 0 \arcdeg . 1 .
This indicates that a significant part of the Galactic center diffuse emission arises from a truly diffuse optically-thin thermal plasma , and not from an unresolved collection of faint X-ray point sources related to the old stellar population .