30 September 2004

Speaker: Meg Urry (Yale University)

Title: In Search of Supermassive Black Holes

Abstract: Active Galactic Nuclei (AGN) are signposts for actively accreting supermassive black holes. AGN are common in the early Universe (z~2-3) but may be undercounted by factors of 3-10 because obscuration by gas and dust prevents their inclusion in UV-excess or optical surveys. With the unprecedented combination of the Spitzer (infrared) Space Telescope, the Chandra X-ray Observatory, and the Hubble Space Telescope, there is now a unique opportunity to find obscured AGN at the epoch of peak black hole accretion and peak star formation. The Great Observatories Origins Deep Survey (GOODS) project, conceived 4 years ago as the deepest multiwavelength probe to date and designed to find obscured AGN at z~2-3, suggests there can be a substantial population of obscured AGN. Once selection biases are taken into account, a fixed ratio of obscured to unobscured AGN is consistent with the redshift distribution in deep X-ray surveys, the apparent decrease in obscured AGN with increasing luminosity, and the integrated X-ray background. We discuss a key test of this picture, namely the far-infrared properties of AGN, in the context of the Spitzer GOODS observations.

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