Stars and Dark Matter in the Halo of the Milky Way

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This work addresses the formation and structure of the Milky Way galaxy with particular focus on the galactic halo. The distribution, kinematics, and chemical composition of halo stars can be used to back-track the formation history of the halo which formed by mergers of small galaxies and star associations. The tidal interaction of the Milky Way galaxy with dwarf galaxies or stellar clusters also led to tidally stripped stars which are now traceable as tidal streams in the galactic halo. This characterizes the galactic gravitational potential from stellar motions and the distribution of dark matter. New tidal streams are searched for and known streams better characterized using photometric and spectroscopic data from the Sloan Digital Sky Survey (SDSS, SDSS II, & SDSS III) and methodologies developed in previous work by the investigators. The results from this study will lead to three dimensional density model of the Milky Way halo, including its smooth component, streams and other substructure, over the 12,600 square degrees of high Galactic latitude sky imaged by the SDSS. The observations are used to build a realistic spatial model of the density distribution of stars in spheroid globular cluster and dwarf galaxy tidal debris streams in the Milky Way?s halo. When combined with radial velocities, these data will better constrain the gravitational potential of the Milky Way. This in turn helps to determine the density structure of the dark matter by matching orbits and N-body simulations to multiple tidal debris streams simultaneously. It is an advantage to consider more than one tidal debris stream at a time and that more realistic potential models are used. Including the distribution properties and density of stars along the tidal debris stream rather than only using their average position and velocity is another advantage for models that aim to constrain the gravitational halo potential and the mass distribution in our galaxy. Two graduate students, and 3 undergraduate student researchers will participate in this project which will help to train the next generation of scientists. The principal investigator has a strong education and outreach program which continues as part of this work. In collaboration with the Dudley Observatory, the Greater Capital Region Teacher Center, and the Summer@Rensselaer program office, twenty-five K-12 teachers will able to take classes to bring astronomy in the class room. This projects also supports the MilkyWay@home web site run by the principal investigator, which directly involves a volunteer computing community of about 40,000 people from 166 countries, who contribute hundreds of TeraFLOPS of computing power to Milky Way research.