Supermassive black holes and the growth of galaxies

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Astronomers have recently discovered that the center of essentially every massive galaxy contains a supermassive black hole (SMBH), and that the properties of SMBHs are tightly correlated with those of their host galaxies. These correlations suggest that the cosmic evolution of SMBHs and their hosts are fundamentally linked, but the details of this connection are still unclear. As an STFC Fellow, I propose to work for three years at Durham University, using data from cutting-edge observatories (such as the Hubble Space Telescope, Chandra X-ray Observatory, Spitzer Space Telescope, Herschel, and SCUBA2) to address key questions about the evolution of SMBHs and galaxies. This work seeks to understand the interplay between galaxies, black holes, and dark matter by observing galaxy and black hole growth at crucial epochs in the early Universe. The first project explores how SMBH accretion and star formation are fueled. This work will be driven by data from Herschel and SCUBA2, powerful new infrared and submillimeter observatories that will allow us to observe fainter and more deeply obscured galaxies than ever before. A prevailing theory is that galaxy and black hole growth is fueled by the major mergers of gas-rich galaxies, which induce vigorous star formation and drive gas down onto the black hole, producing an active galactic nucleus (AGN) that is highly obscured by gas and dust. There have recently been discovered distant galaxies at redshift 2 that have high rates of star formation and obscured AGN, but there is not yet direct evidence that they are powered by mergers. Herschel and SCUBA2 data will allow us to perform the first direct tests of the merger-fueling hypothesis, by measuring the spatial correlations between large samples of highly obscured AGN and surrounding galaxies. Preliminary results from my current research suggest that moderately obscured AGN are indeed associated with mergers, since they have an excess of nearby galaxies on small scales. My proposed work will perform the same test for deeply buried AGN that are expected to be the immediate products of mergers. The second project will address the role of large-scale structures on SMBH and galaxy evolution. Recent theory and observations suggest that there is a characteristic dark matter halo mass for which mergers are most common and AGN feedback actively quenches the formation of stars. Some studies at low redshifts, including my own recent research, are consistent with this picture, but it has not been tested in massive structures at high redshifts where AGN activity is at its peak. Making use of the Durham group's recent ultradeep X-ray observations of a protocluster at redshift 3, I will measure the local galaxy density around X-ray detected AGN to test if accretion is enhanced in environments where mergers are most common. I also plan to analyze near-infrared spectra of the AGN in the protocluster, to constrain the nature and abundance of energetic outflows that could halt star formation and heat intergalactic gas. Both these projects, by making use of cutting-edge observational and theoretical tools, will help us understand how our Milky Way galaxy, and other galaxies we observe in the local Universe, came to exist. In addition to research, I also plan to work to help enhance the public's understanding of the cosmic history of the Universe. In the past I have enjoyed giving public lectures to astronomy groups and schools in the U.S., and would look forward to presenting the latest results to the British public as well. I have corresponded with a number of amateur astronomy societies in northern England, and expect to be able to schedule talks every 1--2 months during the term of the Fellowship, in order to directly promote public enthusiasm for this exciting research and for science in general.