AAS 203rd Meeting, January 2004
Session 129 Pierce Prize Lecture
Invited, Thursday, January 8, 2004, 11:40am-12:30pm, Centennial I/II

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[129.01] The Most Distant Quasars: Probing the End of Cosmic Dark Ages

X. Fan (University of Arizona)

Since its first discovery four decades ago, distant quasars have always been one of the most important tools to understand the evolution of the universe. Studies of the highest redshift quasars probe the relation between the formation of the earliest supermassive black holes and galaxies. The quasar absorption lines trace the evolution of the intergalactic medium, and reveal when and how the reionization process happened, ending the cosmic dark ages. I will present recent results using the high-redshift quasar sample from the Sloan Digital Sky Survey (SDSS). More than 400 quasars at z>4 have been discovered in the SDSS, including eleven at z>5.7, with the highest redshift of z=6.42. Using this large sample, we show that the density of quasars decline rapidly towards high-redshift. Meanwhile, their spectral properties show little evolution, indicating early chemical enrichment in the quasar environment. They also show strong signs of on-going star-formation from their dust and gas emissions, suggesting the co-evolution of first generation black holes and galaxies. The absorption spectra of the highest-redshift quasars show strong evolution of Ly \alpha optical depth at z>5.5. Complete Gunn-Peterson troughs have been detected in quasars at z>6.2.This indicates that the neutral fraction of the IGM begins to increase rapidly, and suggests that we might be reaching the tail end of the reionization process. The combination of the IGM measurements from SDSS quasars and CMB polarization measurements from WMAP can be used to probe the detailed history of reionization.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.