AAS 206th Meeting, 29 May - 2 June 2005
Session 14 Astrophysics with Optical Interferometry
Poster, Monday, 9:20am-6:30pm, Tuesday, 10:00am-7:00pm, May 30, 2005, Ballroom A

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[14.13] Probing Galactic Dark Matter With SIM Observations of Tidal Tails

S.R. Majewski (U. Virginia), J. N. Bahcall (IAS), D. Geisler, W. Gieren (U. Concepcion), E. K. Grebel (Astr. Inst. Basel), C. J. Grillmair (Caltech/SIRTF Sci. Cen.), K. V. Johnston (Wesleyan U.), D. R. Law (Caltech), R. J. Patterson, A. A. Polak (U. Virginia), I. N. Reid (STScI), D. N. Spergel, T. Sumi, S. Tremaine (Princeton U.)

The nature of the dark matter that composes 90 Galaxy remains a profound mystery. Astronomical observations can provide crucial insight on this fundamental issue by probing the large-scale spatial distribution of dark matter, addressing, in particular, the following questions: Is dark matter in our Galaxy centrally concentrated and lumpy as predicted for cold dark matter (such as the lightest SUSY particles or axions) or is it more smoothly distributed and less lumpy? Is the overall shape of the dark matter halo oblate (Johnston, Law & Majewski 2005, ApJ, 619, 800), prolate (Helmi 2004, ApJ, 610, L97) or triaxial (Newberg & Yanny 2004, AAS, 205, 142.04)? What is the total mass and extent of the Milky Way, and what is its corresponding role in the dynamics of the Local Group? We intend to tackle these questions directly, through observations of stars in objects whose dynamics reflect the large-scale Galactic potential: satellite galaxies, star clusters, and halo tidal streams. Measuring the motions of dynamical tracers in the outer Galaxy demands proper motions accurate to better than 10 microarcsecond yr-1 at magnitudes V > 18. NASA's SIM PlanetQuest is the only currently planned mission that can provide such data. SIM observations of the well-mapped Sagittarius star stream will, in addition, provide a definitive determination of the rotation speed of the Sun, pinning down the scale of the Galactic rotation curve to constrain the mass distribution in the inner Milky Way.

Funded by NASA/JPL contract 1228235 for the Taking Measure of the Milky Way Key Project for SIM PlanetQuest.

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