X-ray probing of the dark matter.

The authors have determined gaseous and gravitational mass of elliptical galaxies and poor and rich clusters of galaxies, combining the data of Ginga and Einstein observatory. The mass of X-ray emitting gas is found to be more dominant than that of stars, while the gaseous mass in galaxies is at most 10% of the stellar mass. The ratio of the gravitational mass to the stellar mass increases as the system size increases. For small systems, such as elliptical galaxies the gravitational mass is only a few times of the stellar mass, while for large systems such as rich clusters, it become more than 20 times of the stellar mass. However, the ratio of the gravitational mass to the luminous mass (sum of the stellar and gaseous mass) is almost constant independent of the system size.