X-ray Study of the Virgo Cluster of Galaxies with ASCA

Hironori Matsumoto

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. We also present the results of the mapping observations of the northwest region of the Virgo cluster. Since the spectra of the M87 regions are complex, an adequate fit requires at least two thin thermal-plasma components. The temperatures of the hot and cool components are approximately 2.9 and 1.3 keV, respectively, and the temperatures of these components are both nearly constant over the central 10' radius from the center of M87. However, the flux of the cool component is more concentrated toward the center than that of the hot component. Furthermore the surface brightness profile of the hot component can be extrapolated smoothly to that of the intracluster medium (ICM) beyond 40' from the center. These suggest that the cool component of M87 can be attributed to the interstellar matter of M87, while the hot component is the ICM of the Virgo main body. The abundances of Fe, Si, and S rise towards the center of M87, although the ratios of Si/Fe and S/Si remain constant. We also found, contrary to the Einstein results, that the abundance ratio of oxygen to iron (O/Fe) is smaller than the solar value. These strongly constrain the chemical evolution scenario. The X-ray spectra of the ICM at regions beyond 40' from the center of M87 can be represented by a single-temperature plasma. The temperature of the ICM decreases with radius from 0' to 50', and it becomes almost constant beyond the 50' radius. The metal abundances also decrease with radius from 0' to 50', then become constant beyond the radius of 50'. These temperature and abundance profiles can be clues to investigate the cluster formation history and cosmological parameters.