• Galaxies in the Local Universe

    Studying galaxies in the local universe allows up to examine them and the processes that drive their evolution at a level of detail that is not possible at higher redshift. In general I have focused on the relationship between gas and stars and how that relationship drives evolution. These studies range from blind HI surveys to studies of the relationship between galaxies and the intergalactic medium to the influence of galaxy environment - pairs, groups, and clusters - on the evolution of galaxies.

    Escape of Ionizing Radiation from Dwarf Galaxies

    After the Big Bang the Universe was hot and dense, but it cooled as it expanded allowing neutral atoms to form. It was only with the first stars, galaxies, and AGN that enough energy was returned to the universe to ionize most of the atoms. It is in this mostly ionized state that the universe remains today. Nevertheless, it is still uncertain which types of objects were most important for the early reionization of the universe, the stellar ionization from galaxies, or the high energy radiation from material falling onto black holes at the centers of AGN. We examine the radiation escaping from nearby, low mass galaxies in an effort to understand how these kind of systems might contribute to reionization.

    VLBA Observations of the Cores and Jets of AGN

    Measuring how Earth is oriented in space is important for the calibration of our GPS system. These measurements required a fixed reference frame that is created through observations of AGN. At the microarcsecond position accuracies that are important for this reference frame, position shifts that are observed as a function of frequency become important. We seek to understand the astrophysics at the interface between the core and jets in these systems that drive these position shifts with frequency.