Wide field weak lensing observations of A1689

Abstract

We present a mass profile for A1689 from 0.13 h^{-1} Mpc < r < 2 h^{-1} Mpc from a weak lensing analysis of a 34'x34' R-band image from the ESO/MPG Wide Field Imager. We detect the gravitational shearing of a 23<R<25.5 background galaxy population even at the edge of the image with a 4-sigma significance, and find a two-dimensional mass reconstruction has a 13.4-sigma significance mass peak centered on the brightest cluster galaxy. This peak is well fit by both a 1028+-35 km/s singular isothermal sphere and a r200 = 1.28 Mpc, c = 6 universal CDM profile, although the universal CDM profile provides a better fit with 95.5% confidence. These mass measurements are lower than most of those derived by other means and we discuss possible reasons for weak lensing providing an underestimate of the true mass of the cluster. We find that the correction factors needed to reconcile the weak lensing mass models with the strong lensing Einstein radius would result is a much larger fraction of faint stars and foreground and cluster dwarf galaxies in the 23<R<25.5 object catalog than is seen in other fields.