The host galaxies of AGN in the Sloan Digital Sky Survey

We summarize recent investigations into the relation between the evolution of black holes and galaxies based on optical spectra from the Sloan Digital Sky Survey. The galaxy population exhibits a remarkably simple bimodal behavior in age and structure as a function of mass. Strong emission-line AGN (Seyferts) inhabit those unusual galaxies that are both relatively massive and dense, yet have a significant young stellar population. A volume average over the SDSS sample, shows that the population of black holes with masses less than ∼107.5 M⊙ is growing rapidly at the current epoch. The population of more massive black holes (“dead QSOs”) is quiescent, with weak activity traced by low-power radio sources. For the population of bulge-dominated galaxies as-a-whole, the volume-averaged ratio of the rates of star formation to black hole accretion in the present universe is of-order a thousand (similar to the ratio of stellar and black hole mass in galaxy bulges today). The processes that established this ratio in the fossil record are still at work today, albeit preferentially in less massive black holes and bulges.