Weak Lensing Analysis of Cl 1358+62 UsingHubble Space TelescopeObservations

Abstract

We report on the detection of weak gravitational lensing of faint, distant background objects by Cl 1358+62, a rich cluster of galaxies at a redshift of z = 0.33. The observations consist of a large, multicolor mosaic of Hubble Space Telescope WFPC2 images. The number density of approximately 50 background objects arcmin-2 allows us to do a detailed weak lensing analysis of this cluster. We detect a weak lensing signal out to~1.5 Mpc from the cluster center. The observed distortion is consistent with a singular isothermal sphere model with a velocity dispersion of 780 ± 50 km s-1. The total projected mass within a radius of 1 Mpc corresponding to this model is (4.4 ± 0.6) × 1014 M☉. The errors given here represent the random error due to the ellipticities of the background galaxies. The uncertainty in the redshift distribution introduces an additional systematic error of ~10% in the weak lensing mass. The weak lensing mass is slightly lower than dynamical estimates and agrees well with X-ray mass estimates. The mass distribution is elongated in a similar way as the light. The axis ratio of 0.30 ± 0.15 and position angle of -21° ± 7° were measured directly from the observations and agree very well with a previous strong lensing determination. A two-dimensional reconstruction of the cluster mass surface density shows that the peak of the mass distribution coincides with the peak of the light distribution. We find a value of (90 ± 13)h50 M☉ L for the mass-to-light ratio, consistent with being constant with radius. The point-spread function of HST is highly anisotropic at the edges of the individual chips. This systematically perturbs the shapes of objects, and we present a method for applying the appropriate correction.