NOAO >   Observing Info >   Approved Programs >   2009A-0423

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Proposal Information for 2009A-0423


PI: Steven R. Majewski, University of Virginia, srm4n@virginia.edu
Address: Astronomy Department, PO Box 400325, Charlottesville, VA 22903-4325, USA

CoI: Ricardo R. Munoz, Yale University
CoI: Sangmo Tony Sohn, Caltech
CoI: Richard J. Patterson, University of Virginia
CoI: Kathryn V. Johnston, Columbia University
CoI: Christopher Palma, Penn State University

Title: A New Problem for (Lambda)CDM on Small Scales: Too Many Tidally Disrupting dSphs?

Abstract: The Sagittarius (Sgr) dwarf galaxy+tidal tail system provides a clear example of a Milky Way (MW) satellite in tidal disruption. But is Sgr the exception or \it paradigm of dSph galaxies? Interesting clues suggest the latter: Other MW dSphs exhibit very extended surface brightness profiles and approximately flat velocity dispersion profiles, as does Sgr out into its tidal arms and as do N-body models of disrupting dSphs. But only in the Carina dSph have we found another clear set of tidal tails (Munoz et al. 2006,2008). Nevertheless, \it yet more tidally disrupting MW dSphs is a problem for CDM, which predicts that nearly all should have their luminous parts securely protected within dark matter cocoons. Thus, it is critical to determine if other dSphs sharing the structural and velocity patterns of Sgr and Carina at inner radii have tidal tails at larger radii. As with our successful Carina study, we made large MOSAIC maps around the Leo I (4.5 deg^2) and Ursa Minor (17 deg^2) dSphs to find tidal tails. While in both cases follow-up spectroscopy reveals numerous velocity dSph members beyond the King radius, definitive tails are not yet outlined. We propose to finish the Leo I and Ursa Minor studies, and determine whether CDM has a new problem on small scales (i.e. that there are too many tidally disrupting dSphs compared to expectations from (Lambda)CDM models).


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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