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 (FBGs), which dominate the shear signal, are relatively more distant. The derived cluster mass is quite sensitive to the N(z) for the FBGs. At one extreme, if all the FBGs are at z_s = 3, then the mass within a 0.5 h^-1 Mpc aperture is (5.9 ± 1.24) × 10¹⁴ h^-1 M_☉, and the mass-to-light ratio is M/L_V = 350 ± 70 h in solar units. For z_s = 1.5 the derived mass is ~70% higher and M/L ≃ 580 h. If N(z) follows the no evolution model (in shape) then M/L ≃ 800 h, and if all the FBGs lie at z_s ≲ 1 the required M/L exceeds 1600 h. 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, for a plausible cluster mass, most of the FBGs must lie at high redshift (z > 1).