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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

Sangmo Tony Sohn·S. R. Majewski·R. R. Muñoz·W. E. Kunkel·K. V. Johnston·J. C. Ostheimer·P. Guhathakurta·R. J. Patterson·M. H. Siegel·M. C. Cooper
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Abstract

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. As in previous papers in this series, we take advantage of photometry in the M, T_2, and DDO51 filter system to select LeoI red giant branch star candidates, and, so far, this selection technique has proven 100% reliable in selecting actual Leo I members among more than 100 M < 21.5 Leo I giant candidates having previous or new Keck DEIMOS spectroscopy to a radius >1.3 times the limiting radius of the fitted, central King profile. The two-dimensional distribution of all similarly-selected Leo I giant candidates is well fitted by a central single-component King profile of limiting radius 13.3 arcmin, but many giant stars are found outside this newly derived King limiting radius. The density profile thus shows a break at a major axis radial distance of ~10 arcmin produced by an excess of stars at and beyond the King limiting radius (spectroscopically confirmed to be made of true Leo I members), and primarily along the major axis of the main body of the rather elongated satellite. This spatial configuration, a rather flat velocity dispersion profile and an asymmetric radial velocity (RV) distribution among the Leo I members at large radii together support a picture where Leo I has been tidally disrupted on at least one, but at most two, perigalactic passages of a massive Local Group member. (abridged)

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Sangmo Tony Sohn, S. R. Majewski, R. R. Muñoz, W. E. Kunkel, K. V. Johnston, J. C. Ostheimer, P. Guhathakurta, R. J. Patterson, M. H. Siegel, M. C. Cooper. 2007-03-17. Exploring Halo Substructure with Giant Stars X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy. https://doi.org/10.1086/518302

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