NOAO >   Observing Info >   Approved Programs >   2003B-0295

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Proposal Information for 2003B-0295


PI: Mike Gladders, Carnegie Institution of Washington (Observatories), gladders@ociw.edu
Address: Carnegie Observatories, Headquarters, 813 Santa Barbara Street,, Pasadena, CA, 91101-1292, USA

CoI: Howard Yee, University of Toronto
CoI: Henk Hoekstra, Canadian Institute for Theoretical Astrophysics
CoI: Erica Ellingson, University of Colorado at Boulder (Astrophysics)

Title: Spectroscopy of Arcs in High Redshift "Super-Lens" Clusters

Abstract: Recent analyses of a sample of 8 strong lensing galaxy clusters selected from the Red-Sequence Cluster Survey (RCS) shows that a sub- population of massive clusters which have unusually high lensing cross sections are likely the dominant cause of lensing by galaxy clusters. This statistical conclusion, based on the redshift distribution of the lensing clusters and the single- to mutiple-arc clusters number ratio, suggests an explanation for the long-standing disagreement between theory and observations of arc counts; the observed order-of-magnitude excess of arcs is due to the contribution of a sub-population of "super- lenses" which have not been seen in previous theoretical modeling efforts. These so-called "super-lenses" appear to occur predominantly at high redshift, and are typified by having multiple bright arcs, but the reason for the lensing boost is not at all clear. We are undertaking a comprehensive observational study in order to understand the source of this enhanced lensing; some Chandra and HST observations are in hand and more are proposed, and we propose here for complementary spectroscopy. These data, in particular Gemini GMOS nod-and-shuffle observations of arcs in the two best multiple-arc clusters, will allow us to use x-ray data in combination with detailed strong-lensing mass modelling to probe the very central regions of these clusters, and hence illuminate the source of this lensing.


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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