NOAO >   Observing Info >   Approved Programs >   2006A-0566

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Proposal Information for 2006A-0566


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

CoI: Ricardo Munoz, University of Virginia
CoI: Richard J. Patterson, University of Virginia
CoI: Chris Palma, Penn State University

Title: Tidal Disruption of Galactic dSphs: A Photometric Test

Abstract: The Sgr dwarf galaxy + tidal tail system, now extensively explored with 2MASS M giants, provides a clear example of a Milky Way satellite in tidal disruption. But is Sgr the exception or the \it paradigm of dSph galaxies? Interesting clues suggest the latter: 1) the other dSph galaxies, like Sgr, have ``King+break" surface brightness profiles; 2) we are finding approximately \it flat velocity dispersions, \sigma_v, from the core out the tidal arms in all dSph galaxies - a trend identical to that seen in Sgr; 3) we have shown that N-body models of a disrupting, low mass dSph - a model that fits the observed morphology and dynamics of Sgr - is equally applicable to other dSphs. However, our conclusions remain tentative given the lack of definitive tidal arms in the other dSphs, a problem that has kept alive the debate on whether the extended, dSph ``break" populations are tidal debris or bound dSph halos. However, we have shown that BHB stars are reliable and easily identifiable tracers of these break populations for some dSphs, especially Ursa Minor. We propose to undertake an extended Mosaic imaging surveys of the Ursa Minor dSph system to determine if its substantial extra-tidal population eventually forms tidal arms or remains azimuthally symmetric - as expected for a bound halo. Our N- body models suggest that tidal arms should become structurally clear beyond about 5 tidal radii of each dSph. In combination with our existing photometry, we can reach these limits in a few nights of Mosaic imaging per dSph.


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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