PI: Chuck Keeton, U. Chicago, firstname.lastname@example.org
Address: Astronomy Department, 5640 S. Ellis Ave., Chicago, IL 60637, USA
CoI: Ann Zabludoff, U. Arizona
CoI: Kurtis Williams, U. Arizona
CoI: Iva Momcheva, U. Arizona
Title: The Importance of Lens Galaxy Environments
Abstract: We are conducting the first comprehensive survey of the environments of all 70 known galaxy-mass gravitational lens systems. Statistical arguments suggest that at least 25% of all lens galaxies should lie in group or cluster environments that introduce biases into lensing analyses. Our proposed MOSAIC imaging is essential to identify galaxies for follow-up spectroscopy to determine which lens galaxies lie in a group or cluster, and to measure the colors and morphologies of member galaxies for evolution studies. The wide field of MOSAIC is also important for discovering mass structures projected ~10\arcmin or more from the line-of-sight, which likely contribute to the lensing potential but were previously ignored. The observations will allow us not only to determine which lenses are significantly affected by environment, but also to use the group membership, velocity dispersion, and centroid to correct and improve the lens models. With the new lens models we will constrain the ellipticity, orientation, and mass profile of lens galaxy dark halos, and to place limits on H_0 and dark energy that complement the standard distance-ladder and CMB results. At the same time, our survey is likely to establish the first systematic sample of poor groups of galaxies out to redshift z=1, which will allow us to study galaxy evolution in these common environments.
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