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A.M. Koekemoer (STScI), GOODS Team
A significant population of supermassive black holes in the early universe has been recently revealed through the discovery of Extreme X-ray / Optical sources (`EXO's). These are active galactic nuclei (AGN) that are well detected in deep X-ray surveys with Chandra and XMM but completely undetected in deep optical imaging with HST and 8-10m ground-based telescopes, to limits that place them at the extreme end of the Fx/Fopt parameter space, with values about 100 times above those typical for AGN. The first mid-IR Spitzer observations of these sources with IRAC and MIPS in the deep GOODS imaging survey has provided detections of these sources, which are combined with the deep optical and near-IR data to investigate their physical nature by means of comprehensive SED modelling. Since these are the only candidates for AGN above redshift 6.5 in the GOODS survey, the resulting discriminating power between low and high-redshift possibilities that is provided by the combined X-ray, HST, near-IR and Spitzer multiwavelength data provides strong constraints on the luminosity function of AGN in the early universe.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.