LENSING FROM THE LIGHT-TRACES-MASS MAP OF MS-1224+20

To compare the gravitational lensing mass with the virial mass of the MS 1224+20 cluster of galaxies, we have completed a uniform, high-precision redshift survey over a field of 7' x 9', obtaining 75 redshifts. The velocity dispersion of 30 cluster galaxies is 770 km s(-1), and the projected harmonic radius is 0.32 h(-1) Mpc. The virial mass is 2.1 x 10(14) h(-1) M,. Correcting for faint cluster galaxies without redshifts and allowing for a modest evolution in the galaxy luminosity function gives a current epoch mass-to-light ratio M/L(V)(0) = 255 h M./L.,, comparable to Coma's 275 h. The same field contains galaxy groups at z = 0.225 and z = 0.412. The clusters' gravitational fields induce image ellipticities that are calculated from the light-traces-mass density distribution and compared with the tangential distortions observed by Fahlman ct al. (1994). Between 1 and 3 virial radii, the observed lensing distortions are [e(T)] = 0.054 +/- 0.017, as compared to the [e(T)] = 0.022 +/- 0.006 that the light-traces-mass model: and the virial M/L predict, hence the gravitational mass of the cluster appears to be at least 2.5 +/- 1.1 times the virial mass.