IMPROVING THE PRECISION OF TIME-DELAY COSMOGRAPHY WITH OBSERVATIONS OF GALAXIES ALONG THE LINE OF SIGHT

In order to use strong gravitational lens time delays to measure precise and accurate cosmological parameters the effects of mass along the line of sight must be taken into account. We present a method to achieve this by constraining the probability distribution function of the effective line-of-sight convergence Kappa sub(ext). The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with Kappa sub(ext) obtained by ray-tracing through structure formation simulations. We explore weighting schemes based on projected distance, mass, luminosity, and redshift. This additional information reduces the uncertainty of Kappa sub(ext) from [sigma] sub( Kappa ) ~0.06 to ~0.04 for very overdense LOSs like that of the system B1608+656. For more common LOSs, [sigma] sub( Kappa ) is reduced to [