Halo Substructure and the Dynamics of Disk Galaxies

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What constitutes a galaxy? The usual image of a large spiral galaxy such as the Milky Way (MW) or Andromeda (M31) shows a rotating disk of stars, gas, dust, spiral arms, and a central bulge. **But beginning in the 1970's, our image of the galaxy swelled as we amassed evidence that galaxies are embedded in extended halos of dark matter. More recently, observations of the outskirt of the MW and M31 have revealed a wealth of stellar structure in the form of satellite galaxies and streams of stars that were tidally stripped from satellites. Finally cosmological simulations of structure formation indicate that dark matter in halos is clumpy, perhaps even more so than the stars.** My research will focus on key aspects of the satellite and subhalo populations. The research is driven, in large part, by the remarkable advances in observations and computational astrophysics and will have implications for the fields of galactic dynamics, cosmological structure formation, and dark matter detection.** Recently, my collaborators and I analysed the distribution of stars in the solar neighbourhood and their motions to reveal what appear to be vertical waves in the MW's disk. We have interpreted this discovery as evidence for a recent and nearby encounter between the MW and one of its satellites. My investigations of these waves will proceed on a variety of fronts. I have obtained additional data, which is being analyzed by graduate students in my group. Other students are using theoretical analysis and numerical simulations to study the interaction of satellite galaxies and stellar disks.** The Pan-Andromeda Archaeological Survey has obtained an unprecedented panoramic picture of M31 and its companion, M33. Our observations suggest that M31 is cannibalizing its satellites while M33 may have had a close encounter with M31 in the recent past. These ideas, bolstered by N-body simulations performed by me and Dubinski (Toronto), help advance our understanding of cosmological structure formation and the distribution of dark matter in the Local Group.********************