My research interests

The fueling of an AGN: an unanswered question
One of the most intriguing, unsolved problems in current cosmology is the question of how the Universe has evolved from a smooth structure into the structure of stars and galaxies that we observe today in the local Universe. A key issue to be addressed is how, and when, the first galaxies formed. This is in turn related to how, and when, the first black holes and active galactic nuclei (AGN) formed. The recently discovered correlation between galaxy bulge and black hole masses suggests that they may form and evolve simultaneously (Magorrian et al. 1998; Merritt & Ferrarese 2001; Merloni, Heinz, & di Matteo 2003; Häring & Rix 2004). Since only a small fraction of galaxies harbor AGN, this correlation also implies that it is not the presence of the black hole that decides whether there is AGN activity or not. Instead, it must depend on the availability of fuel, the efficiency of transporting fuel to the nuclear regions, or the efficiency of releasing energy into radiation. One of the most important problems in AGN research today is how to reveal the processes that trigger and maintain nuclear activity.

Existing morphological and kinematical data of the AGN central environment, including the accretion disk and the obscuring torus, is unfortunately limited, both in resolution and (in the optical) because of obscuration, and it is therefore crucial to develop alternative techniques for investigating the nuclear fuel supply. At radio wavelengths, emission and absorption by the ionized, atomic and molecular components of the ISM can be studied. In particular, applying radio Very Long Baseline Interferometry (VLBI) techniques to study the structure, kinematics and excitation of the nuclear ISM is the only means available to directly probe pc and sub-pc scale regions of AGN. One example is the sub-pc scale, warped accretion disk in NGC4258, probed via water masers (Miyoshi et al. 1995; Herrnstein et al. 1999; Herrnstein et al. 2005; Argon et al. 2007). My research focuses on using radio and millimeter interferometric techniques to study the properties of circumnuclear gas in AGN and starbursts, and the connection between AGN and starbursts.