Weak lensing analysis of C1 1358+62 using Hubble Space Telescope observations

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 Hubb le Space Telescope WFPC2 images. The number density of approximately 50 bac kground objects arcmin(-2) allows us to do a detailed weak lensing analysis of this cluster. We detect a weak lensing signal out to similar to 1.5 Mpc from the cluster center. The observed distortion is consistent with a sing ular 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 thi s model is (4.4 +/- 0.6) x 10(14) M.. The errors given here represent the r andom error due to the ellipticities of the background galaxies. The uncert ainty in the redshift distribution introduces an additional systematic erro r of similar to 10% in the weak lensing mass. The weak lensing mass is slig htly lower than dynamical estimates and agrees well with X-ray mass estimat es. The mass distribution is elongated in a similar way as the light. The a xis ratio of 0.30 +/- 0.15 and position angle of -21 degrees +/- 7 degrees were measured directly from the observations and agree very well with a pre vious 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)h(50) M. L-V.(-1) for the mass-to-light ratio, consistent with being constant with radius. The point-spread function of HST is highly anisotropi c at the edges of the individual chips. This systematically perturbs the sh apes of objects, and we present a method for applying the appropriate corre ction.