ASCA and ROSAT data of the Centaurus cluster , holding a cD galaxy NGC 4696 , were analyzed , as a partial re-analysis after Fukazawa et al .
( 1994 ) , Fabian et al .
( 1994 ) , and Allen & Fabian ( 1994 ) .
Radial brightness profiles in different energy bands show that the central excess emission of this cluster , known previously in soft X-rays ( < 4 keV ) , is present also in the hard energy band up to 10 keV .
Therefore the central excess emission can not be explained solely by a temperature drop together with a King-type potential having a flat core , and requires a deeper central potential .
A double- \beta brightness distribution gives a good account of the data .
A deprojected energy spectrum within a spherical region of radius \sim 30 kpc at the cluster center indicates that the ICM can not be isothermal there .
Simultaneous fitting of the three ( PSPC , GIS , and SIS ) energy spectra extracted from the central region within a projected radius of 3 arcmin showed that a two-temperature model that has temperatures of 1.4 keV and 4.4 keV and a common metallicity of 1.0 solar with the Galactic absorption gives the best description to the spectra .
A cooling-flow spectral model did not give satisfactory fit .
These results reconfirm the two-phase picture developed by Fukazawa et al .
( 1994 ) in which the hot ICM fills nearly the entire cluster volume , wherein a small amount of cooler plasma is intermixed and localized near the cluster center .
A 3-dimensional cluster model incorporating the two-phase picture , the double- \beta brightness distribution , and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully .
The spatial distribution of the dark matter that is derived by subtracting the stellar mass from the calculated total-gravitating mass deviates from a King-type profile and exhibits a central excess .
Another two-phase cluster model in which the dark-matter density profile is given with the universal density profile ( Navvaro , Frenk , & White 1996,1997 ) also gave a satisfactory account to the data .
A detailed comparison of the iron mass distribution with that of the stellar component reveals that the iron is more widely spread than stars , which may have been caused by energetic supernovae and the motion of the cD galaxy .
Since the derived characteristics of the cool phase including the temperature , angular extent , gas mass , and metallicity , are on a smooth extension of those of inter-stellar medium ( ISM ) of elliptical galaxies , the cool phase can be regarded as the ISM associated with the cD galaxy , while the high X-ray luminosity of the cool phase ( 1.1 \times 10 ^ { 43 } ergs s ^ { -1 } in 0.5–4.0 keV ) is interpreted as a result of a compression by the surrounding hot phase .
The cool-phase X-ray emission is presumably sustained by energies dissipated by infalling mass to the cD galaxy in the course of cluster evolution .