NOAO >   Observing Info >   Approved Programs >   2004B-0235

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Proposal Information for 2004B-0235


PI: Kurtis A. Williams, U. Arizona, kurtis@as.arizona.edu
Address: Steward Obs., 933 N Cherry Ave, Tucson, AZ 85721, USA

CoI: Ivelina Momcheva, U. Arizona
CoI: Charles Keeton, U. Chicago
CoI: Ann Zabludoff, U. Arizona

Title: The importance of lens galaxy environments

Abstract: Statistical arguments suggest that >25% of gravitational lens galaxies lie in groups, which bias lensing results on galaxy dark matter halos, the Hubble constant, and dark energy. To remove these biases, we are conducting the first comprehensive survey of the environments of all known galaxy-mass lenses. We have already obtained imaging for 42 lens fields. \emphHere we propose to finish the imaging for this survey. MOSAIC imaging is essential to identify galaxies for follow-up spectroscopy. For lenses in dense regions, measurement of the group membership, velocity dispersion, and projected centroid will constrain the ellipticity, orientation, total mass, and mass profile of the lens galaxy dark halo, and allow robust limits on H_0 and dark energy that complement the standard distance-ladder and CMB results. Our survey will also create the first large, homogeneous sample of poor groups out to z=1, allowing us to study galaxy evolution in these common environments directly. Our initial results are spectacular - \it we have discovered new groups around at least five lenses, tripled the galaxy membership of three others, and used environment to resolve the long-standing quad-to-double lens discrepancy.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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