Dr. Aaron Barth at the University of California, Irvine, will undertake a program to provide new constraints on the correlation between black hole mass and host galaxy velocity dispersion, and on the mass function of supermassive black holes. The work will incorporate two complementary areas for research. Dynamical measurements of black hole masses will be performed for the most massive nearby galaxies, to provide new constraints on the upper end of the black hole mass function (above 109 solar masses). The other research area involves a study of the population of galaxies with black holes having masses below 106 solar masses, including new measurements of the black hole masses in these objects and new observations to determine the structure of their host galaxies.
Dr. Barth will also undertake efforts targeted toward the expansion and enhancement of the undergraduate astrophysics program at UC Irvine, with a new initiative to integrate research training into the curriculum. He will co-create and teach a new undergraduate observational astronomy laboratory course for junior or senior-level undergraduates. The goal is to give students a hands-on introduction to research methods and prepare them to undertake senior thesis work and summer research projects in observational astronomy. As a major part of the development of the new lab course, Dr. Barth will add new capabilities to his astronomical image viewing and analysis software, written in the IDL image-processing language. This software, called ATV, has been freely available on the World Wide Web for the past six years and is widely used for interactive display and analysis of astronomical images in both educational and research environments at universities and observatories worldwide.
This project encompassed several related research programs designed to study black holes in galaxy centers. The largest aspect of this work was the Lick AGN Monitoring Project, a project which used the method of "reverberation mapping" to measure the distribution of ionized gas on scales of a few light-days surrounding supermassive black holes in active galaxies, and to use the results to determine the masses of the black holes. Our work comprised the largest single observational program ever carried out at the University of California's Lick Observatory, with an allocation of 64 nights at the Lick Shane 3-meter telescope in 2008. Using the reverberation method, we were able to obtain successful measurements of black hole masses for 10 nearby active galaxies in 2008 and 2010, and the black hole masses in these galaxies are in the range of 1 million to 30 million solar masses. This result represents a significant increase in the number of black hole masses measured by the reverberation technique, particularly in this mass range where few measurements had previously been done. Our best data was obtained for the galaxy Arp 151, and for this galaxy we were able to carry out the most detailed studies to date of the motions of ionized gas clouds within the innermost few light-days around a supermassive black hole. Another aspect of this project involved direct measurements of the masses of black holes in nearby galaxies using observations from the Hubble Space Telescope and ground-based telescopes. We carried out a detailed examination of the dynamics of ionized gas in the centers of several nearby elliptical galaxies. For the galaxy Messier 84, which contains a central, rotating disk of ionized gas, we used Hubble Space Telescope observations of the orbital motion of this gas disk to measure the mass of the central black hole, finding a result of 850 million solar masses for this object. We used the adaptive optics system at the Keck Observatory to measure the properties of stellar orbits around the black hole in the center of the galaxy NGC 3998, and found that this galaxy contains a central black hole of mass 810 million solar masses (with 25% uncertainty). We also examined black hole masses in some spiral galaxies to study the low end of the black hole mass distribution. For the spiral galaxy NGC 3621, analysis of Keck Observatory data indicated that the central black hole in this galaxy must have a mass smaller than 3 million solar masses. A major topic of research for this project was examination of the physical properties and host galaxies of black holes with low masses, below around 1 million solar masses. We carried out a detailed study of the galaxy POX 52, which is the first known example of a dwarf elliptical galaxy containing a central black hole, using observations from the Hubble Space Telescope, the Chandra X-ray Observatory, and other facilities, and found that the central active black hole is a highly variable source of X-ray emission and has a likely mass of around 300,000 solar masses. We also used Keck Telescope observations to study a newly discovered set of low-mass, active galaxies found in the Sloan Digital Sky Survey, which provide new evidence that spiral galaxies even smaller than the Milky Way can contain central black holes. We found evidence for two (and possibly three) black holes in the galaxy NGC 3341. In this object, two dwarf galaxies are merging into a large spiral galaxy and one of the dwarf galaxies contains a central black hole that is currently in an highly active phase. This is one of the nearest and best examples of an "offset active nucleus" where an active black hole has been found off-center within a larger host galaxy, providing a snapshot of how galaxy mergers can bring intermediate-mass black holes into a larger galaxy where they will eventually merge with the larger black hole in the center. This NSF grant supported the doctoral thesis work of two graduate students at UC Irvine and the work of one postdoctoral researcher, as well as several undergraduate research students. Between 2007 and 2012, the work supported by this grant was described in 32 publications in the Astrophysical Journal and other scientific journals. The grant also supported the development of a new advanced undergraduate astronomy lab course at UC Irvine that has been offered annually since 2008, and supported the ongoing development of software for visualization and analysis of astronomical images that is used widely in research and educational programs in the United States and internationally.
