Discovery of an Abundance Gradient in the Central Region of the Virgo Cluster

Abstract
We present the ASCA results of spatially resolved X-ray spectra in the central regions of the Virgo cluster, near to the central elliptical galaxy M87 and 40' northwest of M87 (M87 NW). Since the spectra of the M87 region is complex, an adequate fit requires at least two thin thermal-plasma components. The temperatures of the hot and cool components are approximately 3.0 and 1.3 keV, respectively, and the temperature of these components are both nearly constant over the central 10' radius from the center of M87. The spectrum of M87 NW, on the other hand, can be well fitted by a single thin thermal-plasma model of ∼ 2.7 keV temperature. The abundances of Fe, Si, and S rise towards the center of M87, though the ratios of Si/Fe and S/Si remain constant. We also found, contrary to the Einstein Observatory's results, that the abundance ratio of oxygen to iron (O/Fe) is smaller than the solar value.

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