Wide-Field Weak Lensing by RX J1347–1145

We present an analysis of weak-lensing observations for RX J1347-1145 over a 43' × 43' 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 < R < 26, we detect a weak-lensing signal at the p < 0.0005 level, finding best-fit parameters of σ_v = 1400 km s^-1 for a singular isothermal sphere model and r₂₀₀ = 3.5 Mpc with c = 15 for an NFW model in an Ω_m = 0.3, Ω_Λ = 0.7 cosmology. In addition, a mass-to-light ratio M/L_R = 90 ± 20 M_☉/L_R☉ was determined. These values are consistent with the previous weak-lensing study of RX J1347-1145 by Fischer & 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 & Kneib.