Detection of weak lensing by a cluster of galaxies at z= 0.83

We report the detection of weak gravitational lensing of faint, distant background galaxies by the rich, X-ray luminous cluster of galaxies MS 1054−03 at z=0.83. This is the first measurement of weak lensing by a bona fide cluster at such a high redshift. We detect tangential shear at the 5% 10% level over a range of radii 50 ∼< r ∼< 250 ′′ centered on the optical position of the cluster. Two-dimensional mass reconstruction using galaxies with 21.5 < I < 25.5 shows a strong peak which coincides with the peak of the smoothed cluster light distribution. Splitting this sample by magnitude (at I = 23.5) and color (at R − I = 0.7), we find that the brighter and redder subsamples are only very weakly distorted, indicating that the faint blue galaxies (FBG’s), which dominate the shear signal, are relatively more distant. The derived cluster mass is quite sensitive to the N(z) for the FBG’s. At one extreme, if all the FBG’s are at zs = 3, then the mass within a 0.5hMpc aperture is (5.9± 1.24)× 10h M⊙, and the mass-to-light ratio is M/LV = 350 ± 70h in solar units. For zs = 1.5 the derived mass is ∼70% higher and M/L ≃ 580h. If N(z) follows the no evolution model (in shape) then M/L ≃ 800h, and if all the FBG’s lie at zs ∼< 1 the required M/L exceeds 1600h. These data provide clear evidence that large, dense mass concentrations existed at early epochs; that they can be weighed efficiently by weak lensing observations; and that most of the FBG’s are at high redshift. Subject headings: cosmology: observations — gravitational lensing — dark matter — galaxies: photometry — galaxies: distances and redshifts — galaxies: clusters: individual (MS 1054−03).