AN X-RAY AND OPTICAL STUDY OF MATTER DISTRIBUTION IN CLUSTERS OF GALAXIES

A sample of 12 Abell clusters of galaxies has been studied in the opti cal and X-ray bands. The optical data are derived from automatic photo metry based on microdensitometric scans of Palomar Schmidt F-band plat es. ROSAT PSPC data were obtained from the public archive. Galaxy dens ity and X-ray luminosity profiles have been constructed and deprojecte d by parametric and nonparametric techniques to obtain volume density profiles. We find a relation between the gas density rho(gas) and the galaxy density rho(gal) consistent with the prediction of the hydrosta tic isothermal model. We confirm that more than 70% of the cluster mas s is dark within 1.5 Mpc h(50)(-1) from the cluster center. Outside 25 0 kpc we find a nearly constant MIL, ratio, which on average is 137 M. /L., implying that the galaxy mass traces the total matter distributio n. The dark mass-to-light ratio has a similar behavior. We also find a baryonic fraction f(b) approximate to 0.2, which, assumed as represen tative of the cosmic value and compared with nucleosynthesis calculati ons, constrains the cosmological parameter Omega(0), to be smaller tha n 0.25.