Four Quasars above Redshift 6 Discovered by the Canada-France High-z Quasar Survey

By C. Willott, P. Delorme, A. Omont, J. Bergeron, X. Delfosse, T. Forveille, L. Albert, Céline Reylé, G. Hill, M. Gully-Santiago and 8 more. 2007

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The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed to locate quasars during the epoch of reionization. In this paper we present the discovery of the first four CFHQS quasars at redshifts greater than 6, including the most distant known quasar, CFHQS J2329-0301 at z = 6.43. We describe the observational method used to identify the quasars and present optical, infrared, and millimeter photometry and optical and near-infrared spectroscopy. We investigate the dust properties of these quasars, finding an unusual dust extinction curve for one quasar and a high far-infrared luminosity due to dust emission for another. The mean millimeter continuum flux for CFHQS quasars is substantially lower than that for SDSS quasars at the same redshift, likely due to a correlation with quasar UV luminosity. For two quasars with sufficiently high signal-to-noise ratio optical spectra, we use the spectra to investigate the ionization state of hydrogen at z > 5. For CFHQS J1509-1749 at z = 6.12 we find significant evolution (beyond a simple extrapolation of lower redshift data) in the Gunn-Peterson optical depth at z > 5.4. The line of sight to this quasar has one of the highest known optical depths at z ≈ 5.8. An analysis of the sizes of the highly ionized near-zones in the spectra of two quasars at z = 6.12 and 6.43 suggest that the intergalactic medium surrounding these quasars was substantially ionized before these quasars turned on. Together, these observations point toward an extended reionization process, but we caution that cosmic variance is still a major limitation in z > 6 quasar observations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7d80bc28e799f9f5b2ff08bf33202b538c7f08da

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Citations in the corpus

BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS (2013, background): “In the past 10 yr, more than 60 quasars at 5.7 z 6.4 have been discovered (e.g., Fan et al. 2006; Jiang et al. 2008, 2009; Venemans et al. 2007; Willott et al. 2007, 2010; Morganson et al. 2012,; Bañados et al. 2014), mainly thanks to optical surveys such as the Sloan Digital Sky Survey (SDSS; York”
Observational evidence for intermediate-mass black holes (2017, unknown): “Quasars with BH masses of up to 1010 M have been detected when the Universe was only 0.8 Gyr old (z ∼ 7, e.g., Fan et al. 2001, 2003; Willott et al. 2007, 2010; Mortlock et al. 2011; Venemans et al. 2013; Wu et al. 2015).”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, background): “…Sky Survey (SDSS; Fan et al. 2000, 2003, 2006, Jiang et al. 2016, Wang et al. 2016, 2017); the Canada-France High-redshift Quasar Survey (CFHQS; Willott et al. 2007, 2009, 2010a,b); the UK Infrared Deep Sky Server (UKIDSS;Venemans et al. 2007, Mortlock et al. 2009); the Dark Energy Survey…”
THE PAN-STARRS1 DISTANT z > 5.6 QUASAR SURVEY: MORE THAN 100 QUASARS WITHIN THE FIRST GYR OF THE UNIVERSE (2016, background): “…(2006), (10) McGreer et al. (2006), (11) Carilli et al. (2007), (12) Kurk et al. (2007), (13) Stern et al. (2007), (14) Venemans et al. (2007), (15) Willott et al. (2007), (16) Jiang et al. (2008), (17) Wang et al. (2008), (18) Jiang et al. (2009), (19) Kurk et al. (2009), (20) Mortlock et al.…”
A SURVEY OF z ∼ 6 QUASARS IN THE SLOAN DIGITAL SKY SURVEY DEEP STRIPE. I. A FLUX-LIMITED SAMPLE AT zAB < 21 (2007, background): “The area and the depth will 3 then be comparable to the CFHQS, which has covered ∼ 400 deg2 to a limit of iAB ∼ 24.5 (Willott et al. 2007).”
STAR FORMATION AND GAS KINEMATICS OF QUASAR HOST GALAXIES AT z ∼ 6: NEW INSIGHTS FROM ALMA (2013, background): “…surveys (e.g., the Sloan Digital Sky Survey [SDSS], Fan et al. 2006; Jiang et al. 2008, 2009; the Canada–France High Redshift Quasar Survey, Willott et al. 2007, 2009, 2010; the UKIDSS Large Area Survey [ULAS], Mortlock et al. 2009, 2011; and the Panoramic Survey Telescope and Rapid…”
THE CANADA–FRANCE HIGH-z QUASAR SURVEY: NINE NEW QUASARS AND THE LUMINOSITY FUNCTION AT REDSHIFT 6 (2009, methodology): “Spectroscopic reductions were performed as detailed in Willott et al. (2007).”
Formation of Supermassive Black Hole Seeds (2016, background): “…z > 6 reveal the existence of supermassive black holes (SMBHs) of a few billion solar masses within the 1 Gyr after the Big Bang (Fan et al. 2006; Willott et al. 2007; Jiang et al. 2008, 2009; Mortlock et al. 2011; Venemans et al. 2013; Bañados et al. 2014; Venemans et al. 2015; Jiang et al.…”
DISCOVERY OF THREE z > 6.5 QUASARS IN THE VISTA KILO-DEGREE INFRARED GALAXY (VIKING) SURVEY (2013, background): “The extended criteria are therefore sensitive for quasars down to the redshift where the highest redshift quasars are found in optical surveys (e.g., Willott et al. 2007).”
EVIDENCE FOR NON-EVOLVING Fe ii/Mg ii RATIOS IN RAPIDLY ACCRETING z ∼ 6 QSOs (2011, background): “…have been discovered (Fan et al. 2000, 2001, 2003, 2004, 2006; Jiang et al. 2008, 2009; Willott et al. 2007, 2010) thanks to the Sloan Digital Sky Survey (SDSS, York et al. 2000) and other large multi-wavelength surveys such as the Canada France High-z Quasar Survey (CFHQS, Willott et al. 2007).”
EDDINGTON-LIMITED ACCRETION AND THE BLACK HOLE MASS FUNCTION AT REDSHIFT 6 (2010, methodology): “The data reduction method is as described in Willott et al. (2007).”
The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6 (2010, methodology): “There is also substantial information on the neutral content of the intergalactic medium (IGM) since z ∼ 6 via observations of the Gunn-Peterson trough (Gunn & Peterson 1965) in quasar spectra (Djorgovski et al. 2001; Becker et al. 2001; Fan et al. 2006; Willott et al. 2007).”
MOLECULAR GAS IN z ∼ 6 QUASAR HOST GALAXIES (2010, methodology): “…published observations of dust con- tinuum at 250 GHz that were made with the Max-Planck Millimeter Bolometer Array (MAMBO, Kreysa et al. 1998) on the IRAM 30m-telescope, and ten of these have been detected (Bertoldi et al. 2003a; Petric et al. 2003; Willott et al. 2007; Wang et al. 2007, 2008b).”
Large Ly α opacity fluctuations and low CMB τ in models of late reionization with large islands of neutral hydrogen extending to z < 5.5 (2018, background): “The effective optical depth (τeff ) of Lyman-α (Lyα) absorption in QSO spectra at redshift z & 5 is observed to exhibit large spatial fluctuations (Fan et al. 2006; Willott et al. 2007; Becker et al. 2015; Barnett et al. 2017; Tang et al. 2017; Bosman et al. 2018; Eilers et al. 2018).”
The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “First, the transmission fraction of z ∼ 6 quasar light blueward of Lyα through the intergalactic medium (IGM) indicates that the Universe was mostly ionized by this epoch (e.g. Gunn & Peterson 1965; Fan et al. 2002, 2006; Willott et al. 2007; Mortlock et al. 2011).”