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Title: Discovery of three z > 6.5 quasars in the VISTA kilo-degree infrared galaxy (VIKING) survey

Studying quasars at the highest redshifts can constrain models of galaxy and black hole formation, and it also probes the intergalactic medium in the early universe. Optical surveys have to date discovered more than 60 quasars up to z ≅ 6.4, a limit set by the use of the z-band and CCD detectors. Only one z ≳ 6.4 quasar has been discovered, namely the z = 7.08 quasar ULAS J1120+0641, using near-infrared imaging. Here we report the discovery of three new z ≳ 6.4 quasars in 332 deg{sup 2} of the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the number from 1 to 4. The newly discovered quasars have redshifts of z = 6.60, 6.75, and 6.89. The absolute magnitudes are between –26.0 and –25.5, 0.6-1.1 mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the Mg II emission line in all three objects. The quasars are powered by black holes with masses of ∼(1-2) × 10{sup 9} M {sub ☉}. In our probed redshift range of 6.44 < z < 7.44 we can set a lower limit on the space density of supermassive black holes of ρ(M {sub BH} > 10{sup 9} Mmore » {sub ☉}) > 1.1 × 10{sup –9} Mpc{sup –3}. The discovery of three quasars in our survey area is consistent with the z = 6 quasar luminosity function when extrapolated to z ∼ 7. We do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z = 6 to z = 7.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ; ;  [5] ;  [6] ;  [7]
  1. Max-Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  2. Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom)
  3. Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, London, E1 4NS (United Kingdom)
  4. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
  5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
  6. MIT-Kavli Center for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
  7. Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden (Netherlands)
Publication Date:
OSTI Identifier:
22348537
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; ASTRONOMY; BLACK HOLES; CHARGE-COUPLED DEVICES; COSMOLOGY; DENSITY; EMISSION; GALAXIES; INFRARED SPECTRA; INFRARED SURVEYS; LUMINOSITY; MASS; QUASARS; RED SHIFT; SPACE; TELESCOPES; UNIVERSE