NOAO >   Observing Info >   Approved Programs >   2002A-0364

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Proposal Information for 2002A-0364


PI: Steven R. Majewski, University of Virginia, srm4n@virginia.edu
Address: P.O. Box 3818, Charlottesville, VA 22903-0818, USA

CoI: Chris Palma, Penn State University
CoI: Eva K. Grebel, Max Planck Institute for Astronomy
CoI: Michael Odenkirchen, Max Planck Institute for Astronomy
CoI: Richard J. Patterson, University of Virginia
CoI: William E. Kunkel, Las Campanas Observatory
CoI: Kathryn V. Johnston, Wesleyan University
CoI: Peter Frinchaboy, University of Virginia

Title: A Curious Pair: The High M/L Dwarf Spheroidal Galaxies Ursa Minor and Draco

Abstract: Large velocity dispersions in dwarf spheroidal (dSph) galaxies are commonly interpreted as evidence of extreme dark matter (DM) domination. Detractors from this viewpoint offer a variety of models wherein mass-to- light (M/L) ratios may be inflated due to tidal effects. The Ursa Minor (UMi) and Draco (Dra) dSphs are most interesting in this regard, as these systems are alike in almost every regard, including extremely high M/L, and yet their structures are completely different: Our wide- field photometric studies reveal UMi to have a clumpy internal structure surrounded by a large number of extratidal stars, indicative of tidal effects and ongoing dissolution. In contrast, Dra shows a smooth, regular density profile, no indication of tidal truncation, and no extratidal material, supporting the notion of a DM-dominated galaxy. We propose to undertake the necessary test of the physics needed to answer the question: Can both the tidal disruption and large DM models explain high dSph M/L values? A variety of DM as well as tidal disruption models can be discriminated by knowing the run of velocity dispersion with radius. Extant radial velocity studies of \it all Galactic dSphs exist only for the cores. We will supplement the existing UMi and Dra core data with the required velocities across the entire known extent of these galaxies.


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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