Katie Merrell

    The exciting and unexpected discovery that supermassive black hole mass scales with host galaxy properties such as bulge stellar velocity dispersion, luminosity, and mass demonstrates the co-evolution of galaxies and their central black holes. The most popular methods for measuring supermassive black hole mass are stellar dynamical modeling and reverberation mapping. My research involves using stellar dynamical modeling to measure supermassive black hole mass within active galactic nuclei. Individual stars in the galactic bulge cannot (currently) be resolved in galaxies other than our own, but we can use IFU spectroscopy to extract stellar bulk motions to study the gravitational influence of the central black hole. Deconvolution of the observed spectra with stellar template spectra is applied to produce line of sight velocity distributions, which represent the stellar kinematics in the black hole potential well. A Swarzschild orbit superposition method is then used to model the stellar orbit structure, from which a black hole mass can be determined. Reverberation mapping on the other hand determines the supermassive black hole virial mass by measuring the time delay between light received from the accretion disk and re-processed light from the broad line region. Though this means reverberation mapping can only be used with active galaxies, it is distance independent. Because stellar dynamical modeling depends on the ability to spatially resolve the innermost region of the bulge, it can only be used with galaxies that are relatively nearby. There are only a handful of galaxies that meet both criteria, and only two have published results from both methods. These special galaxies are the key to refining these black hole mass measurement methods. Obtaining agreeable masses will inevitably lead to a more precise understanding of how supermassive black holes grow and evolve with their host galaxies.