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M.G. Walker, M. Mateo (University of Michigan), E.W. Olszewski (The University of Arizona, Steward Observatory), X. Wang, M. Woodroofe (University of Michigan)
Dwarf spheroidal (dSph) galaxies are the smallest stellar systems for which Newtonian gravity implies the presence of a dark matter component. This makes dSphs objects of fundamental importance within the prevalent framework of \LambdaCDM structure formation. The dSphs are thought to be embedded within dark matter halos that happened to survive the merger assembly of larger systems, and thus represent the most pristine nearby relics from earlier epochs of cosmological structure. The proximity of the Milky Way's ~10 known dSph satellites provides the unique opportunity to measure the radial velocities of individual dSph stars, enabling detailed kinematic studies. Velocity samples containing precision measurements for tens of stars established that the internal kinematics of at least some dSphs are dominated by dark matter. More recent work based on samples of ~200 stellar velocities has begun to address the details of mass distribution, the degree of velocity anisotropy, and the influence of external tidal forces imposed on dSphs by the Milky Way.
Here we present large new samples of dSph velocities obtained using the Michigan-MIKE Fiber System at the Magellan telescopes. We have measured precise (±3 km s-1) line-of-sight velocities for 330 members of the Carina dSph, 325 members of the Fornax dSph, 285 members of the Sextans dSph, and 675 members of the Sculptor dSph. We discuss various analysis methods and apply a new nonparametric technique we have developed in order to estimate mass distributions from samples containing large numbers of discrete velocities. We find strikingly similar mass profiles over the radial region common to each sample.
This work is supported by generous grants from the National Science Foundation and the University of Michigan's Horace H. Rackham School of Graduate Studies.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.