CfA Colloquium: May 29, 2003

Speaker: Tim Heckman (Johns Hopkins)

Title: Spectroscopy of 10^5 Galaxies: Implications for Cosmic Gastro-Physics

Abstract: We now have a very successful and tightly constrained model for the cosmic evolution of the structure of dark matter. The challenge is now to understand the ``gastrophysics'' by which the luminous baryons in the universe are painted onto the dominant dark matter component. This requires understanding the gas/star/black-hole ecosystem. The on-going Sloan Digital Sky Survey (SDSS) affords us the opportunity to examine the fossil record of galaxy and black hole evolution with unparalleled precision. I will summarize recent work based on optical spectra of 122,808 SDSS galaxies. I will describe the methodology we have developed 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. We also find that the most powerful active nuclei inhabit those rare galaxies that are both massive and relatively young. I will briefly discuss some of the implications of these results.

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