NOAO >   Observing Info >   Approved Programs >   2002A-0265

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Proposal Information for 2002A-0265


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

CoI: Ann Zabludoff, University of Arizona
CoI: Emilio Falco, Smithsonian Astrophysical Observatory
CoI: Joseph Lehar, MIT Whitehead Institute

Title: Discovering Poor Groups with Strong Lensing

Abstract: Although poor groups of galaxies are the most common environment for galaxies, and are important sites for continuing galaxy evolution, little is known about groups beyond z ~ 0.1; traditional survey techniques cannot identify distant group candidates and confirm that they are bound systems. Gravitational lensing offers a new method for simultaneously identifying and confirming distant groups, because in many galaxy-mass strong lens systems the lens models require that the lens galaxy lie in an extended structure like a group. We propose to survey all known galaxy-mass lenses to discover groups at redshifts z ~ 0.3-1. By combining color-magnitude diagrams with lens models to identify candidate groups, we will establish the first systematic sample of at least 10-20 distant groups. For each candidate group, we will select magnitude-limited samples of galaxies for follow-up spectroscopy to identify group members. We expect to confirm 10-20 members per group and study their colors, morphologies, and spectral characteristics. Using the redshift baseline in our sample, and comparing with existing samples of nearby groups and distant clusters, we will study environmental effects in galaxy evolution. With these pencil-beam surveys, we will greatly improve lens models by including the effects of the groups as well as any structures along the line of sight; we will use the models to robustly measure the shapes of galaxy dark matter halos and test models of galaxy formation, and to improve lensing measurements of the Hubble constant. In this semester we will complete the imaging for 48 lenses, or 80% of the known lenses.


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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