TIM HECKMAN, JOHN HOPKINS UNIVERSITY

PRINCETON ASTRONOMY COLLOQUIUM - FEBRUARY 22, 2005

ABSTRACT

The Co-Evolution of Galaxies and Black Holes: an SDSS Perspective

I will summarize a recent investigation into the relation between the evolution of black holes and galaxies on based on SDSS optical spectra of over 200,000 galaxies.

I will describe the methodology we use to measure the basic properties of these galaxies and of the active nuclei (accreting black holes) present in many of them. We find that galaxies exhibit a remarkably simple bimodal behavior in their ages and structure as a function of their mass. Optically-powerful active nuclei (Seyfert nuclei) inhabit those unusual galaxies that are both relatively massive and young.

Performing a volume average over the SDSS sample, I will show that the population of black holes with masses less than 100 million M_sun is growing rapidly at the current epoch. The population of more massive black holes (``dead quasars'') is quiescent, with low-level activity traced by low-power radio sources.

For massive 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 be at work today, albeit preferentially in less massive black holes and bulges.