Title: A Kinematic Study of the Sagittarius Stream using the Michigan/Magellan Fiber System

Abstract:
The orbital motion of the Sagittarius Stream is dictated by the extended distribution of dark 
matter in the Milky Way. Yet the shape of this dark matter distribution is widely debated. Not 
only do different dynamical tracers (ie. extended HI, halo stars, dwarf galaxies, tidal streams) 
produce widely different results, but even studies that focus solely on the Sagittarius Stream 
disagree on the extent and shape of the halo (ie. spherical, oblate, prolate, or triaxial). A further 
complication is the morphology of the progenitor of the stream, which also plays a role in 
shaping the positions and velocities of stars in the Stream. Three different scenarios have been 
proposed: 1) the progenitor was a single dwarf spheroidal galaxy, 2) the progenitor was a single 
dwarf irregular/spiral galaxy with ordered rotation, 3) the progenitor was a pair of smaller 
gravitationally bound galaxies that fell in together. By comparing models of the stream to 
spectroscopic observations, I hope to determine the morphology of the progenitor galaxy and 
thereby eliminate one of the variables that makes it so hard to deduce the shape of the Milky 
Way dark matter halo. To complete this large-scale spectroscopic survey, I am using the 
Michigan/Magellan Fiber System (M2FS), a wide-field fiber-fed spectrograph. I will present the 
first observational results of this dissertation project.