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Exploring Halo Substructure with Giant Stars. X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy

Sohn, Sangmo Tony and Majewski, Steven R. and Muñoz, Ricardo R. and Kunkel, William E. and Johnston, Kathryn V. and Ostheimer, James C. and Guhathakurta, Puragra and Patterson, Richard J. and Siegel, Michael H. and Cooper, Michael C. (2007) Exploring Halo Substructure with Giant Stars. X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy. Astrophysical Journal, 663 (2). pp. 960-989. ISSN 0004-637X. doi:10.1086/518302.

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We present a wide-field (4.5 deg^2) photometric and spectroscopic survey of the Leo I dwarf spheroidal (dSph) galaxy to explore its extended morphology and dynamics. To select Leo I red giant branch star candidates we exploit M, T_2, and DDO51 filter photometry; this yields 100% pure Leo I stars among more than 100 M < 21.5 Leo I giant candidates having previous or new Keck spectroscopy. The two-dimensional distribution of all photometric Leo I giant candidates is well fitted by a single-component King profile of limiting radius 13.4' out to a major axis radial distance of ~10', but beyond this point the density profile shows an excess of stars along the major axis of the main body. This spatial configuration, together with a rather flat velocity dispersion profile and an asymmetric radial velocity distribution among Leo I members at large radii, supports a picture where Leo I has been tidally disrupted on one or two perigalactic passages about a massive Local Group member. We demonstrate this hypothesis using mass-follows-light, N-body simulations of satellites in a Milky Way-like potential that reproduce the observed structural and dynamical properties of Leo I remarkably well. These models include ~3 × 10^7 solar mass, tidally disrupting dSphs on bound orbits with rather high eccentricity (0.93-0.96) and small perigalactica (10-15 kpc). The simulations yield an observationally constrained orbit for Leo I without the measurement of its proper motion. Given the overall success of our satellite models to account for the observed properties of Leo I, we conclude that there is no need to invoke an extended dark matter halo around the satellite and that an overall modest M/L for the satellite is consistent with the available data.

Item Type:Article
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Majewski, Steven R.0000-0003-2025-3147
Johnston, Kathryn V.0000-0001-6244-6727
Guhathakurta, Puragra0000-0001-8867-4234
Cooper, Michael C.0000-0003-1371-6019
Additional Information:© 2007 The American Astronomical Society. Received 2005 December 5; accepted 2007 March 15. The authors wish to thank Chris Palma for providing several useful computer programs and Alison Coil for aiding the Keck DEIMOS observations. The referee has provided a number of useful comments that have improved the paper. Support for this work at Virginia was provided by NSF grants AST 97-02521 and AST 03-07851, a Cottrell Scholar Award from the Research Corporation, NASA/JPL contract 1228235, the David and Lucile Packard Foundation, and the generous support of The F. H. Levinson Fund of the Peninsula Community Foundation. K. V. J.’s contribution was supported through NASA grant NAG5-9064 and NSF CAREER award AST 01-33617. M. H. S. received thesis travel support from KPNO that was used during the collection of the Mosaic data and support from the STScI Director’s Discretionary Research Fund.
Funding AgencyGrant Number
NSFAST 97-02521
NSFAST 03-07851
Research CorporationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
F. H. Levinson Fund of the Peninsula Community FoundationUNSPECIFIED
Subject Keywords:galaxies : evolution; galaxies : halos; galaxies : individual (Leo I); galaxies : interactions; galaxies : photometry; galaxies : structure
Issue or Number:2
Record Number:CaltechAUTHORS:20091116-151242172
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Official Citation:Exploring Halo Substructure with Giant Stars. X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy Sangmo Tony Sohn, Steven R. Majewski, Ricardo R. Muñoz, William E. Kunkel, Kathryn V. Johnston, James C. Ostheimer, Puragra Guhathakurta, Richard J. Patterson, Michael H. Siegel, and Michael C. Cooper 2007 ApJ 663 960-989 doi: 10.1086/518302
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16719
Deposited By: Tony Diaz
Deposited On:25 Nov 2009 21:34
Last Modified:08 Nov 2021 23:29

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