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The Washington Research Foundation Fellowship

Meghin Spencer, Astronomy and Physics, 2011-12 WRFF

Meghin Spencer photoThe field of astronomy has been an integral part of my life for, quite literally, as long as I can remember. Over the years, spectacles such as meteor showers, comet passings, eclipses and planet transits only heightened my excitement. Therefore, it seemed natural that I major in astronomy and physics at the University of Washington. It is here that I learned how much more there is to the study than what meets the (unaided) eye. By involving myself with an array of research projects, ranging from low mass stars to planetary nebulae to spiral galaxies, and studies of both the radio and optical regimes, I feel I have extremely broadened my undergraduate knowledge.

Though I have spent a significant amount of time exploring the different subGfields of astronomy through research and other activities, the project that I have dedicated the majority of my time to pertains to something that we can’t even see: dark matter. Discovered in 1934, its nature remains one of the most pressing scientific mysteries of the modern era, a bothersome fact considering dark matter accounts for about 85% of the total matter in the universe. My project focuses on constraining the amount of dark matter within large spiral galaxies under the guidance of Drs. Zeljko Ivezic and Peter Yoachim. While most studies rely on dynamical tracers such as neutral hydrogen gas, planetary nebulae, or globular clusters to map out the gravitational well of a galaxy, my study uses satellite galaxies. It is a relatively new technique because the amount of detected satellites around any given spiral galaxy is generally not sufficient to accurately determine its mass. However, recent searches within the SDSS database reveal that this may not be the case, especially for galaxy NGC 4258. By spectroscopically observing galaxies that could potentially be satellites with the Apache Point Observatory 3.5Gmeter telescope, I can determine whether they are in fact satellites or simply high redshift galaxies, and use those measurements to produce an estimate for the galaxy’s total mass. This research will be presented in the 219th American Astronomical Society meeting in Austin, Texas next January, and should lead to a published paper.

Next year I plan on attending graduate school so that I can obtain a Ph.D. in astronomy.

I am incredibly thankful to the Washington Research Foundation for this fellowship, without which I could not present this research to the greater astronomy society.

Mentor: Peter Yoachim, Astronomy

Project Title: Utilizing Satellite Galaxies to Understand the Nature of Dark Matter

Abstract: I propose to estimate the mass of the extended dark matter halo of nearby spiral galaxy NGC 4258 by measuring the velocity dispersion of its satellite galaxy system. This galaxy is particularly interesting because it is similar in size to the Milky Way, and has the largest amount of known satellites for any galaxy outside the Local Group. Before I began, I searched the Sloan Digital Sky Survey (SDSS) database and found 15 satellite galaxies that already have spectra. I then made a list of target satellite galaxies, 34 of which I was able to observe in 5 half-nights with the 3.5-meter APO telescope. By combining my measurements with those already taken, I can make a reasonable conclusion on the dark matter halo mass. Next, I intend to make further observations with the Wisconsin Indiana Yale and NOAO (WIYN) telescope. These additional satellite galaxies will provide me with around 40 good velocity measurements, enabling me to constrain the dark matter halo mass to within a 25% error. I will write a computer program that will be able to automatically reduce the WIYN data so that similar studies in the future can be completed with more ease. The research proposed here will be especially useful during the era of the Large Synoptic Survey Telescope (LSST) when other galaxy systems containing large amounts of satellite galaxies will become accessible to similar type studies due to the enhanced telescope magnification. This work is anticipated to yield a preliminary presentation in the January American Astronomical Society (AAS) meeting and a refereed paper in the Astrophysical Journal by the end of the next academic year.