DETERMINING GRAVITATIONAL MASSES OF GALAXY CLUSTERS WITH VIRIAL EQUILIBRIUM AND ARC-LIKE IMAGES

The mass derived from gravitational lensing reflects the total mass contained in the lensing system, independent of the specific matter contents and states. A comparison of the dynamical masses from hydrostatic equilibrium with the gravitational masses from arclike images of background galaxies is made for four clusters of galaxies at intermediate redshifts. It is found that virial analysis has underestimated the total duster masses (from lensing) by a factor of similar to 3-6 within a radius of similar to 0.3 Mpc h(50)(-1) around the cluster centers, indicating that clusters of galaxies might not be regarded as the well-relaxed virialized systems. The increase of the total cluster masses obtained from lensing leads to the decrease of the baryon fractions of clusters of galaxies, which provides a clue to solving the ''Omega(0) discrepancy puzzle'' in cosmology.