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Date: Wednesday, December 14, 2011
Speaker: Jim Braatz, National Radio Astronomy Observatory, Charlottesville, VA
Topic: Supermassive Black Holes and Precision Cosmology with Megamasers
Time and Location: 1:00 PM, with Q&A to follow; in a 1st floor conference room at the American Center for Physics, 1 Physics Ellipse, College Park, MD-- off River Rd., between Kenilworth Ave. and Paint Branch Parkway.
Abstract: In the gaseous and dusty accretion disks that surround supermassive black holes in the nuclei of nearby galaxies, water molecules emit maser radiation at a wavelength of 1.3 cm. Applying the technique of Very Long Baseline Interferometry, we can map the distribution of individual maser clouds in these disks and determine their positions with an accuracy better than 0.01 milli-arcseconds, and their line-of-sight velocities with an accuracy better than 1 km/s. The masers thus provide a powerful tool for tracing the dynamics of the disk. We use these data to measure precise masses of the central black holes, a measurement which has important implications in understanding how galaxies evolve. In some cases we can also use them to measure direct, geometric distances to the host galaxies, and thereby get a geometric measurement of the expansion rate of the universe. Complementing other observations, these measurements will help to place significant constraints on models of dark energy.
Biography: Jim Braatz is an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesvile, VA. A native Marylander, Jim received a B.A. in Physics from the Johns Hopkins University and a Ph.D. in Astronomy from the University of Maryland. Subsequently he was a postdoc at Harvard and then a Jansky Fellow with NRAO in Green Bank, WV. Jim has worked on development of the Green Bank Telescope and is also a member of the North American ALMA Science Center, helping the astronomical community use the new Atacama Large Millimeter/Submillimeter Array (ALMA). Jim's research is centered on observations of radio emission from active galaxies. He is the PI of the Megamaser Cosmology Project.