Dr. Kate Brand
STScI

University of Florida Astronomy Colloquium - Sept. 26th, 2007

The accretion history of SMBHs and nature of optically faint ULIRGs

How did the mass of 10^9-10^10 solar mass super-massive black holes at the center of massive galaxies in the local Universe build up? Did the bulk of the growth happen in an optically luminous AGN phase? Or did a substantial fraction of SMBH growth occur in a dusty, obscured phase, visible as a luminous infrared galaxy? Has there been substantial SMBH growth in a radiatively inefficient regime after the more luminous AGN phase? These are particularly important questions given the tight relationship between the mass of galaxy bulges and their SMBHs, suggesting that the formation and evolution of galaxies and SMBHs are intimately linked. I will use the multi-wavelength data in the NDWFS Bootes field to address this issue. First, I will present an X-ray stacking analysis of ~20,000 red galaxies between z~0-1 to show that the nuclear accretion rates in these sources are either low or radiatively inefficient and are declining with time. I will then discuss the nature of an extreme, obscured population of ULIRGs at z~2-3. I will present near-IR and mid-IR spectroscopy from Keck, Gemini, and Spitzer of such sources and show that they are likely to be sources undergoing a period of rapid and substantial growth in both their bulge and SMBH mass.