1ST DETECTION OF A GRAVITATIONAL WEAK SHEAR AT THE PERIPHERY OF CL-0024+1654

We report on the first measurement out to 1.5 h100(-1) Mpc from the ce nter of a coherent gravitational shear of faint objects around the clu ster lens Cl 0024 + 1654. Ultra-deep CCD images taken in subarcsecond seeing conditions at the Canada-France-Hawaii Telescope show biased di stributions of ellipticity and orientation that are interpreted as gra vitational distortion of the observed images of background sources by the cluster. The shear intensity decreases radially, and from its patt ern we infer that the center of the mass distribution coincides with t he optical center. Assuming a power law for the projected mass profile , we constrain its slope to range between 0.7 and 1.2. The data are co mpatible with the Isothermal Sphere (IS) model, although a de Vaucoule ur law (dVc) reasonably fits the observations. For the IS model, the c ore radius is below 20'', with marginal agreement out to 40'', and no cutoff radius is seen in the range of the data. The two models may be distinguished by measuring the shear field beyond 15' with twice the p resent accuracy. The total mass within an Abell radius reaches the lar ge value of 2 x 10(15) h100(-1) M. (IS) or 1.2 x 10(15) h100(-1) M. (d Vc). We predict the typical redshift of sources to be z = 0.7-0.8 for the IS but z > 1.2 for dVc.