NOAO >   Observing Info >   Approved Programs >   2004A-0209

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Proposal Information for 2004A-0209


PI: Chuck Keeton, U. Chicago, ckeeton@oddjob.uchicago.edu
Address: Astronomy Department, 5640 S. Ellis Ave., Chicago, IL 60637, USA

CoI: Ann Zabludoff, U. Arizona
CoI: Iva Momcheva, U. Arizona
CoI: Kurtis Williams, U. Arizona

Title: The Importance of Lens Galaxy Environments

Abstract: Statistical arguments suggest that > 25% of gravitational lens galaxies lie in groups or clusters that introduce biases into lensing analyses. To remove these biases, we are conducting the first comprehensive survey of the environments of all 70 known galaxy-mass lenses. 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 also reveals mass structures projected along the line-of-sight, which likely contribute to the lensing potential but were previously ignored. With our survey, we will determine those lenses significantly affected by environment and use the group membership, velocity dispersion, and centroid to correct and improve the lens models. We will then constrain the ellipticity, orientation, and mass profile of lens galaxy dark halos, and place limits on H_0 and dark energy that complement the standard distance- ladder and CMB results. Our survey will also create the first systematic sample of poor groups of galaxies out to z=1, allowing us to study galaxy evolution in these common environments directly. The first results from our previous MOSAIC and spectroscopic runs are spectacular - we have discovered new groups around at least five lenses, tripled the galaxy membership of three others, and demonstrated a link between environment and the long-standing quad-to-double lens discrepancy. \it Here we propose to complete the MOSAIC imaging for the survey.


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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