Hubble Space Telescope Weak-Lensing Study of the z=0.83 Cluster MS 1054-03

Abstract

We have measured the weak gravitational lensing of faint, distant background 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 number density of background galaxies obtained in these observations result in an accurate and well-calibrated measurement of the lensing induced distortion. The strength of the lensing signal depends on the redshift distribution of the background galaxies. We used photometric redshift distributions from the northern and southern Hubble Deep Fields to relate the lensing signal to the mass. The predicted variations of the signal as a function of apparent source magnitude and color agrees well with the observed lensing signal. 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)x10¹⁵ h^-1₅₀ M_solar within an aperture of radius 1 h^-1₅₀ Mpc. Under the assumption of an isothermal mass distribution, the corresponding velocity dispersion is 1311⁺⁸³_-89 km s^-1. For the mass-to-light ratio we find 269+/-37 h₅₀ M_solar/L_Bsolar after correcting for passband and luminosity evolution. The errors in the mass and mass-to-light ratio include the contribution from the random intrinsic ellipticities of the source galaxies, but not the (systematic) error due to the uncertainty in the redshift distribution. However, the estimates for the mass and mass-to-light ratio of MS 1054-03 agree well with other estimators, suggesting that the mass calibration works well. The reconstruction of the projected mass surface density shows a complex mass distribution, consistent with the light distribution. The results indicate that MS 1054-03 is a young system. The timescale for relaxation is estimated to be at least 1 Gyr. We have also studied the masses of the cluster galaxies, by averaging the tangential shear around the cluster galaxies. Using the Faber-Jackson scaling relation, we find the velocity dispersion of an L_* galaxy (L_B=8x10¹⁰ h^-2₅₀ L_Bsolar for MS 1054-03) is 203+/-33 km s^-1. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.