Collaborative Research: A New Era of Mapping Dark Matter in Dwarf Spheroidal Galaxies

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AST 0206081MateoDwarf spheroidal galaxies (dSph) are likely to be the smallest systems in the Universe which contain both dark matter and luminous matter. The dark matter content and distribution in dSphgalaxies can be studied in detail if one can collect enough kinematic data to constrain models. Dr. Mario Mateo, at the University of Michigan, and Dr. Edward Olszewski, at the University of Arizona, will use three new technologies to make a factor of 10-30 advance in the number of stellar velocities measured per galaxy. The goal is no longer to weigh the dSph's, but to derive the distribution of mass, thus the distribution of the dark matter. While small steps have been taken towards that goal to date, with heroically collected samples of up to 200 stars, it is only withsubstantially larger samples that reasonable models will be distinguished from each other. Suchmapping of the mass within dSph galaxies is required to critically compare their dark-matter haloswith the many - sometimes contradictory - predictions of models of galaxy and large-scale structure formation in the Universe. These researchers will use a new telescope - the Magellan 6.5-meter telescope of Las Campanas Observatory in Chile - a new echelle spectrograph - the Magellan-Inamori-Kyocera Echelle (MIKE) spectrograph - and a new 256-fiber system to feed this spectrograph a large number of stars simultaneously. This instrumental combination will allow the collection of 750-1500 kinematic samples per galaxy. ***