Rutgers University Astrophysics Seminar

ABSTRACT: Quasars are powerful probes of the high-redshift Universe, although previously none were known beyond a redshift of z > 6.5 because they have been identified primarily in optical surveys. Using data from the UKIRT Infrared Deep Sky Survey (UKIDSS), it has been possible to search beyond this optical limit, although the resultant samples of candidate quasars are highly contaminated by scattered Galactic stars. This problem was overcome using a Bayesian selection/ranking scheme, resulting in the identification of a dozen z >~ 6 quasars and one, ULAS J1120+0641 at z = 7.085, with z > 6.5. ULAS J1120+0641 hosts a 2x109 M_Sun black hole, the formation of which just 0.8 Gyr after the Big Bang places significant restrictions on the possible models of black hole growth. The small visible size of the ionized "near zone" around the quasar, combined with a Ly alpha transmission profile that is consistent with a damping wing, provide strong evidence that the neutral fraction of the inter-galactic medium around the quasar was f_HI > 0.1.