Wide‐Field Weak Lensing by RX J1347−1145

We present an analysis of weak-lensing observations for RX J1347-1145 over a 43\u27 × 43\u27 field taken in B and R filters on the Blanco 4 m telescope at CTIO. RX J1347-1145 is a massive cluster at redshift z = 0.45. Using a population of galaxies with 20 \u3c R \u3c 26, we detect a weak-lensing signal at the p \u3c 0.0005 level, finding best-fit parameters of σv = 1400 km s-1 for a singular isothermal sphere model and r200 = 3.5 Mpc with c = 15 for an NFW model in an Ωm = 0.3, ΩΛ = 0.7 cosmology. In addition, a mass-to-light ratio M/LR = 90 ± 20 M☉/LR☉ was determined. These values are consistent with the previous weak-lensing study of RX J1347-1145 by Fischer \u26 Tyson, giving strong evidence that systemic bias was not introduced by the relatively small field of view in that study. Our best-fit parameter values are also consistent with recent X-ray studies by Allen et al. and Ettori et al. but are not consistent with recent optical velocity dispersion measurements by Cohen \u26 Kneib