Two-phase intracluster medium in the Centaurus Cluster of galaxies

ASCA and ROSAT data of the Centaurus Cluster, containing a cD galaxy NGC 46 96, were analyzed in a partial reanalysis of the work of Fukazawa et al., F abian et al., and Alien & Fabian. Radial brightness profiles in different e nergy bands show that the central excess emission of this cluster, seen pre viously in soft X-rays (<4 keV), is also present in the hard energy band up to 10 keV. Therefore, the central excess emission cannot be explained sole ly by a temperature drop together with a King-type potential with a flat co re, and requires a deeper central potential. A double-beta brightness distr ibution gives a good account of the data. A deprojected energy spectrum wit hin a spherical region of radius similar to 30 kpc at the cluster center in dicates that the ICM cannot be isothermal there. Simultaneous fitting of th e three (PSPC, GIS, and SIS) energy spectra extracted from the central regi on within a projected radius of 3' showed that a two-temperature model with temperatures of 1.4 and 4.4 keV and a common metallicity of 1.0 solar, wit h the Galactic absorption, gives the best description of the spectra. A coo ling-flow spectral model did not give a satisfactory fit. These results rec onfirm the two-phase picture developed by Fukazawa et al., in which the hot ICM fills nearly the entire cluster volume, where a small amount of cooler plasma is intermixed and localized near the cluster center. A three-dimens ional cluster model incorporating the two-phase picture, the double-beta br ightness distribution, and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully. The spatial distribution of the d ark matter that is derived by subtracting the stellar mass from the calcula ted total gravitating mass deviates from a King-type profile and exhibits a central excess. Another two-phase cluster model in which the dark matter d ensity profile is given with the universal density profile of Navarro, Fren k, & White also gave a satisfactory account of the data. A detailed compari son of the iron mass distribution with that of the stellar component reveal s that the iron is more widely spread than stars, perhaps as a result of en ergetic supernovae and the motion of the cD galaxy. Since the derived chara cteristics of the cool phase, including the temperature, angular extent, ga s mass, and metallicity, are on a smooth extension of those of the interste llar 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 x 10(43) ergs s(-1) in 0.5-4.0 keV) is interpreted as a result of compression by the surrounding hot phase. The cool-phase X-ray e mission is presumably sustained by energies dissipated by mass infalling to the cD galaxy in the course of cluster evolution.