Professor, Astronomy & Astrophysics

I study our own Milky Way galaxy to find out how and why it evolved to its present state. The evidence is that our Galaxy is a fairly typical spiral galaxy. That means that by studying our home in the universe, we can learn a lot about the evolution of other spiral galaxies like it. We can also use the story of our own Galaxy to help interpret observations at high redshift, where we can catch galaxies in the process of forming.

There are lots of observational and theoretical reasons why we think Galaxies like the Milky Way are created through merging and accretion of smaller systems. We can use the Milky Way to help answer some basic questions about how that process works.

What? Did the Galaxy accrete mostly gas which it later turned into stars, or did it accrete a substantial number of stars that formed elsewhere before becoming part of the Galaxy?
When? When were the last few "major" accretion events and how did they shape the observed properties of today's Milky way?
How? We know the Galaxy has a sparse, spherical stellar halo make up of metal-poor stars, a thick disk population or populations of intermediate metallicity, and a old thin disk. How did those stellar populations come to be distributed as they are in the Galaxy?
Because we live in the middle of it, we see stars in the Galaxy spread over the whole sky. You can see that for yourself when you look at the Milky Way stretched across the sky on a clear night. What you are looking at is the disk of our Galaxy, edge-on, from the sun's position near one edge. So if we want a big-picture view of the Galaxy, we need large-area surveys that cover an appreciable fraction of the sky.

Two such surveys I have worked on and with are the Sloan Digital Sky Survey (SDSS) and SEGUE, the Sloan Extension for Galactic Understanding and Exploration. Both of these use imaging in five filters and moderate-resolution spectroscopy to map out the structure (where the stars are) and stellar population content (where stars of different ages and metal-content are located). The SDSS was designed primarily to map the local universe, so it looked up out of the plane of the Galaxy. In the process of doing that extragalactic survey, it mapped about one quarter of the sky around the North Galactic pole. SEGUE is designed specifically to cover a larger range in Galactic latitude, reaching much closer to the plane of the Galaxy, in order study the Milky Way.

Academic Bio
B.S.E., Electrical Engineering, Princeton University
Ph. D., University of Chicago, Astronomy and Astrophysics

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