Determining the Hubble Constant from the Gravitational Lens PG 1115+080
Abstract
The quadruple gravitational lens PG 1115+080 cannot be fit by a single ellipsoidal mass distribution, but it can be well fit by adding a perturbation from the nearby group of galaxies. With the existing constraints, there are degeneracies in the models with respect to the radial profiles of the galaxy and the group and with respect to the position of the group, so that a wide range of models give fits with \chi^2/N_{DOF} < 1. We find H_0=60 \pm 17 km/s/Mpc (1\sigma) for a reasonable range of models. Smaller uncertainties in H_0 can be achieved by reducing the standard errors in the lens galaxy position from 50 mas to 10 mas, by reducing the the uncertainties in the time delays from 3.4 days to 0.5 days, and by constraining the lens mass distribution using HST photometry and the fundamental plane.Keywords
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