Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of the recombining plasma in the south of the Galactic center;
  a relic of the past Galactic center activity?   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 ~42' x
16' centered at (l, b) ~ (0.0, -1.4), 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 cannot be fitted with a plasma in CIE, leaving
hump-like residuals at ~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 x elapsed time) of 5.3 x 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 (~8 kpc
distance). The size of the plasma, the mean density, and the thermal energy are
estimated to be 97 pc x 37 pc, 0.16 cm^-3, and 1.6 x 10^51 erg, respectively.
We discuss possible origins of the recombination-dominant plasma as a relic of
past activity in the GC region.

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The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
3
The categories of this paper are: physics
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The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
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The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con