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Technical Summary

I am interested in studying Local Group dwarf galaxies and the interstellar medium. Please see an (automatically generated) list of publications on NASA ADS here. I am a part of the Galactic Arecibo L-Band Feed Array (GALFA-HI) Survey team, a high resolution, all Arecibo sky survey of neutral hydrogen at LSR velocities of -700 to 700. The high resolution of the survey allows us to probe discrete objects deeper into Galactic emission than has been previously possible. The full data set for Data Release 1 is available to the public. Using this data, I collaborated to create a catalog of approximately 2000 discrete, isolated HI clouds using an semi-automated algorithm (Saul 2011, submitted). Most of these clouds are very likely to be associated with the Milky Way, although their origins are not well understood. My particular interest are those clouds which have structural or kinematic characteristics which make them more likely to be undiscovered Local Group galaxies. Out of the catalog, I identified a population of dwarf galaxy candidates whose characteristics are similar to those of Leo T, the only known ultra-faint galaxy known to contain HI. Some of these candidates lie in the region of sky covered by the Sloan Digital Sky Survey (SDSS), and so a preliminary search for a stellar population at that position can be conducted. One of the candidates showed an apparent stellar population in its color magnitude diagram compared to an equal-area control annulus around the cloud position (Grcevich 2012, in prep). Follow up photometric observations are planned for this and the other candidates. In addition to my observational work, I also also run hydrodynamic simulations of the interaction of the gaseous component of dwarf galaxies with a diffuse hot halo like that of the Milky Way. The code used is Proteus, and is currently implemented in 2D. I found that dwarf galaxies can lose a significant fraction of their gas in less than an orbital timescale due to dynamical stripping even when the traditional ram-pressure criterion for total stripping is not met.

Non-Technical Summary

My research focuses on nearby, small galaxies which are called Local Group dwarf galaxies. One thing I focus on is the gas in these galaxies as well as the gas in our Galaxy, the Milky Way. The faintest of these galaxies, the "ultra-faint" dwarf galaxies, are about a hundred thousand times less massive than the Milky Way and a millions times fainter. Many nearby, ultra-faint dwarf galaxies which were too dim to be seen previously have been discovered in the past eight years. Studying the population of ultra-faint dwarf galaxies is important because there is a major discrepancy between theories of dark matter and what astronomers have observed. Dark matter is called "dark" because it doesn't give off or interact with light - we only see it via its gravitational effects. The leading dark matter theories predict there should be a very large number of low-mass clumps of dark matter near our Galaxy, and since we think galaxies should form in most of these dark matter clumps, it is surprising we don't see a greater number of small galaxies in our Galactic neighborhood. It's not clear if this is because the dark matter predictions are wrong, our understanding of how dark matter clumps become galaxies is incomplete, the galaxies in those dark matter clumps are just too faint for us to have seen them, or some combination of these explanations. One of my current projects is to look for some of these "missing" satellite galaxies. I'm going about this in a new way; in the past these galaxies have been discovered first via their stars, while I am searching for them first by looking at the hydrogen gas they might contain. I am using a large map of neutral hydrogen gas to search for gas clouds that are similar in structure to gas in the dwarf galaxies that we already know about. Then I am searching for concentrations of faint stars at those locations to see if these clouds really are previously unknown galaxies. So far, I have found a number of promising dwarf galaxy clouds, and one even shows evidence for the type of stars one would expect in a small galaxy. I also work on computer simulations of the gas in dwarf galaxies. The Milky Way sits in a big cloud of hot gas which is not very dense. Dwarf galaxies orbit the Milky Way and as they do so their gas interacts with the hot gas of the Milky Way. Usually this causes the gas in the small galaxy to be swept away from its associated dark matter clump. Since stars are formed out of gas, this sweeping effect can affect how many stars are formed in the dwarf galaxies. Since the number of stars determines how a bright a galaxy is, this effect might have a significant impact on what these galaxies look like.