First detection of a gravitational weak shear at the periphery of CL 0024+1654

Abstract

We report on the first measurement out to 1.5 h_100_^-1^ Mpc from the center of a coherent gravitational shear of faint objects around the cluster lens Cl 0024+1654. Ultra-deep CCD images taken in subarcsecond seeing conditions at the Canada-France-Hawaii Telescope show biased distributions of ellipticity and orientation that are interpreted as gravitational distortion of the observed images of background sources by the cluster. The shear intensity decreases radially, and from its pattern we infer that the center of the mass distribution coincides with the 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 compatible with the Isothermal Sphere (IS) model, although a de Vaucouleur law (dVc) reasonably fits the observations. For the IS model, the core 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 present accuracy. The total mass within an Abell radius reaches the large value of 2 x 10^15^ h_100_^-1^ M_sun_ (IS) or 1.2 x 10^15^ h_100_^-1^ M_sun_(dVc). We predict the typical redshift of sources to be z = 0.7-0.8 for the IS but z > 1.2 for dVc.