NOAO >   Observing Info >   Approved Programs >   2004B-0400

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Proposal Information for 2004B-0400


PI: Taro Sato, University of California, Santa Barbara, taro@physics.ucsb.edu
Address: Department of Physics, Broida Hall, Building 572, Santa Barbara, CA 93106-9530, U.S.A.

CoI: Crystal L. Martin, University of California, Santa Barbara

Title: Near-Infrared Imaging of Infalling Galaxies in Abell 851

Abstract: Local environment has a strong effect on the star formation history (SFH) and morphology of galaxies, the observation first recognized in the cores of rich clusters. More recent work indicates the transformation begins at cluster-centric radii beyond the cluster virial radius. Since the cluster environment samples a wide range in the local galaxy density and relative velocities, the dominant physical process driving the transformation evolves over the infall period. Since dwarf galaxies tend to react more strongly to tidal perturbations, an important aide in identifying the dominant physical mechanism is the differential response of dwarfs and massive galaxies to cluster tidal fields. While much progress has been made recently in quantifying the transformation of galaxies in moderately distant (i.e., z ~ 0.5) clusters, the effort has focused exclusively on the population of massive galaxies. This thesis compares the transformation of dwarf galaxies to that of more massive galaxies in Abell 851 (Cl0939+4713; z=0.4). We have obtained KECK LRIS and DEIMOS spectra of over 300 cluster members of which most are fainter than the r ~eq 22 limit of most recent studies, yielding a rich information on the cluster SFH. We request near-infrared imaging suitable for morphological studies and stellar mass mapping. These Gemini/NIRI queue observations of our bluest cluster members will reveal whether the underlying population includes a bulge and/or underlying spiral structure, which would help to identify cluster dwarfs by analyzing with the brightness of the old stellar population. In addition, we request long-term status to obtain 6 nights of KPNO-4m/FLAMINGOS time between 27 January and 1 March of 2005 to image a field extending beyond the cluster virial radius with complete spatial coverage. These infrared images will provide a map of the stellar mass density for comparison to our maps of the star formation rate/history.


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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