Hubble Space Telescope weak-lensing study of the z=0.83 cluster MS 1054-03

We have measured the weak gravitational lensing of faint, distant backgroun d galaxies by MS 1054-03, a rich and X-ray luminous cluster of galaxies at a redshift of z = 0.83, using a two-color mosaic of deep WFPC2 images. The small corrections for the size of the point-spread function and the high nu mber density of background galaxies obtained in these observations result i n an accurate and well-calibrated measurement of the lensing induced distor tion. The strength of the lensing signal depends on the redshift distributi on of the background galaxies. We used photometric redshift distributions f rom the northern and southern Hubble Deep Fields to relate the lensing sign al to the mass. The predicted variations of the signal as a function of app arent source magnitude and color agrees well with the observed lensing sign al The uncertainty in the redshift distribution results in a 10% systematic uncertainty in the mass measurement. We determine a mass of (1.2 +/- 0.2) x 10(15) h(50)(-1) M. within an aperture of radius 1 h(50)(-1) Mpc. Under t he assumption of an isothermal mass distribution, the corresponding velocit y dispersion is 1311(-89)(+83) km s(-1). For the mass-to-light ratio we fin d 269 +/- 37 h(50) M./L-B. after correcting for passband and luminosity evo lution. The errors in the mass and mass-to-light ratio include the contribu tion from the random intrinsic ellipticities of the source galaxies, but no t the (systematic) error due to the uncertainty in the redshift distributio n. However, the estimates for the mass and mass-to-light ratio of MS 1054-0 3 agree well with other estimators, suggesting that the mass calibration wo rks well. The reconstruction of the projected mass surface density shows a complex mass distribution, consistent with the light distribution. The resu lts indicate that MS 1054-03 is a young system. The timescale for relaxatio n is estimated to be at least 1 Gyr. Ne have also studied the masses of the cluster galaxies, by averaging the tangential sheer around the cluster gal axies. Using the Faber-Jackson scaling relation, we find the velocity dispe rsion of an L* galaxy (L-B = 8 x 10(10) h(50)(-2) L-B. for MS 1054-03) is 2 03 +/- 33 km s(-1).