Spatially Resolving the AGN Broad Emission Line Region

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Black holes millions to billions of times the mass of the sun occupy the centers of most galaxies. Hot gas falling onto these supermassive black holes radiates light, which can be bright enough for Astronomers to detect out to large distances corresponding to early stages in the history of the Universe. The mass of the central black hole informs our understanding how galaxies and black holes form and grow. The current method used to measure it depends on the assumption that fast moving gas is in orbit around the black hole. This project will test this basic assumption using data with sufficiently high angular resolution to see the gas motions directly. It will determine whether the gas is falling onto and growing the black hole, or flowing outwards and escaping. The observations will be assisted by monitoring using telescopes on the CU Boulder campus. The monitoring observations will be used to train students both inside and outside the classroom in astronomical observing, and particularly to provide early research experiences for undergraduates from traditionally underrepresented backgrounds.In this project the PI and team will use new data from the Very Large Telescope Interferometer beam combiner instrument GRAVITY to spatially resolve the kinematics and structure of the broad emission line region for a sample of 11 bright Type 1 AGN. Using kinematic models, they will measure the broad emission line radius and establish an interferometric radius-luminosity relation as an independent comparison to those obtained using reverberation mapping. From the modeling results they will infer the emission line region structure and the central black hole mass. In a few cases where both types of measurements exist, they will combine their results with those from velocity-resolved reverberation mapping to carry out detailed studies of the broad emission line structure and kinematics. The same data provide measurements of hot dust structure, which will be used to study the physical connection between the hot dust and atomic gas on sub-milliarcsecond scales. They will also develop and apply kinematic models of disk winds, including where the line emission is optically thick, to determine whether the dominant emission line kinematics is a result of a continuous outflow, or part of the inflow feeding the supermassive black hole. The VLTI/GRAVITY observations critically depend on visible AO performance, which is related to the variable optical brightness. The investigators will use visible wavelength monitoring observations using two 20" telescopes at the Sommers-Bausch Observatory on the CU Boulder campus to assist in target selection.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.