The Growth of Black Holes: From Primordial Seeds to Local Demographics

The properties of local active galaxies provide important constraints on the formation and evolution of supermassive black holes (BHs) and their host galaxies. We have found the first sample of intermediate-mass (10⁴-10⁶ solar mass) BHs in active galaxies; their mass spectrum and radiative properties provide the only currently available observational constraints on the properties of seed BHs in the early universe. We are thus able to measure the BH mass and Eddington ratio distributions of local broad-line active galaxies, including masses as low as 10⁵ solar masses, and infer the current growth modes of BHs as a function of mass. We also examine the relation between BH mass and bulge stellar velocity dispersion (the M-sigma relation) for an unprecedented number of active galaxies, and discuss how differences between the M-sigma relation of active and inactive galaxies reflect the continuing evolution of the BH-bulge system.