We report Suzaku results for soft X-ray emission to the south of the Galactic center ( GC ) .
The emission ( hereafter “ GC South ” ) has an angular size of \sim 42 \arcmin \times 16 \arcmin centered at ( l, b ) \sim ( 0. \arcdeg 0 , -1. \arcdeg 4 ) , and is located in the largely extended Galactic ridge X-ray emission ( GRXE ) .
The X-ray spectrum of GC South exhibits emission lines from highly ionized atoms .
Although the X-ray spectrum of the GRXE can be well fitted with a plasma in collisional ionization equilibrium ( CIE ) , that of GC South can not be fitted with a plasma in CIE , leaving hump-like residuals at \sim 2.5 and 3.5 keV , which are attributable to the radiative recombination continua of the K-shells of Si and S , respectively .
In fact , GC South spectrum is well fitted with a recombination-dominant plasma model ; the electron temperature is 0.46 keV while atoms are highly ionized ( kT = 1.6 keV ) in the initial epoch , and the plasma is now in a recombining phase at a relaxation scale ( plasma density \times elapsed time ) of 5.3 \times 10 ^ { 11 } s cm ^ { -3 } .
The absorption column density of GC South is consistent with that toward the GC region .
Thus GC South is likely to be located in the GC region ( \sim 8 kpc distance ) .
The size of the plasma , the mean density , and the thermal energy are estimated to be \sim 97 ~ { } { pc } \times 37 ~ { } { pc } , 0.16 cm ^ { -3 } , and 1.6 \times 10 ^ { 51 } erg , respectively .
We discuss possible origins of the recombination-dominant plasma as a relic of past activity in the GC region .