Weak Lensing Analysis of CL 1358+62 Using Hubble Space Telescope Observations

September 1998 • 1998ApJ...504..636H

Authors • Hoekstra, Henk • Franx, Marijn • Kuijken, Konrad • Squires, Gordon

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^-1_Vsolar 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.

Based on observations with the NASA ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555

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Gordon Squires

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