THE CANADA–FRANCE HIGH-z QUASAR SURVEY: NINE NEW QUASARS AND THE LUMINOSITY FUNCTION AT REDSHIFT 6

By C. Willott, P. Delorme, Céline Reylé, L. Albert, J. Bergeron, D. Crampton, X. Delfosse, T. Forveille, J. Hutchings, R. McLure and 2 more. 2009

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We present discovery imaging and spectroscopy for nine new z ∼ 6 quasars found in the Canada–France High-z Quasar Survey (CFHQS) bringing the total number of CFHQS quasars to 19. By combining the CFHQS with the more luminous Sloan Digital Sky Survey sample, we are able to derive the quasar luminosity function from a sample of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function shows a slightly lower normalization and flatter slope than found in previous work. The binned data also suggest a break in the luminosity function at M1450 ≈ −25. A double power-law maximum likelihood fit to the data is consistent with the binned results. The luminosity function is strongly constrained (1σ uncertainty <0.1 dex) over the range −27.5 < M1450 < −24.7. The best-fit parameters are Φ(M*1450) = 1.14 × 10−8 Mpc−3 mag−1, break magnitude M*1450 = −25.13, and bright end slope β = −2.81. However, the covariance between β and M*1450 prevents strong constraints being placed on either parameter. For a break magnitude in the range −26 < M*1450 < −24, we find −3.8 < β < −2.3 at 95% confidence. We calculate the z = 6 quasar intergalactic ionizing flux and show it is between 20 and 100 times lower than that necessary for reionization. Finally, we use the luminosity function to predict how many higher redshift quasars may be discovered in future near-IR imaging surveys.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0a123ffb005c1b91f62131c8203850fecf2b7244

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The VISTA deep extragalactic observations (VIDEO) survey (2012, background): “Deeper optical surveys have since been pushing further down the QSO luminosity function (e.g. Willott et al. 2010), but pushing to higher redshifts is impossible with optical surveys, regardless of depth, due to the fact that the Gunn–Peterson trough occupies all optical bands at z > 6.5.”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, background): “By extrapolating measurements of the luminosity function of quasars at redshift z ∼ 6, Willott et al. (2010) estimated number densities out to z = 9.”
The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “3 https://github.com/gkulkarni/QLF/blob/master/Data/allqlfs.dat M1450 > −26.73 to avoid overlapping with Yang et al. (2016); (4) for Willott et al. (2010) and Kashikawa et al. (2015), the redshift intervals were recomputed using consistent completeness estimations.”
Faint high-redshift AGN in the Chandra deep field south: the evolution of the AGN luminosity function and black hole demography (2011, methodology): “At medium to high redshift, we used the distributions of Trakhtenbrot et al. (2011), Shemmer et al. (2004), Netzer & Trakhtenbrot (2007), and Willott et al. (2010b).”
REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, methodology): “If we take the ionizing emissivity estimates that Willott et al. (2010) derive from their deep z ∼ 6 search, extrapolate to z∼8, and adjust their result upwards by 0.2 dex to account for the steeper faint-end slope of α = −2 found at z ∼ 5 by McGreer et al. (2013: versus an assumed faint-end slope…”
Semi-implicit scheme for treating radiation under M1 closure in general relativistic conservative fluid dynamics codes (2012, background): “…accretion state may be responsible for much of the SMBH mass growth in the Universe; for instance, it might explain the paradox of having 109 M BHs already at z > 6, when the Universe was less than 1 Gyr old (Barth et al. 2003; Willott et al. 2005, 2010; Fan et al. 2006; Mortlock et al. 2011).”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, methodology): “This is slightly steeper than the slopes found above from the fit to all data points, but is consistent with the value b = -2.81 reported by Willott et al. (2010b).”
The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields (2025, neutral): “These sources have luminosities that are 2 – 3 dex below that of bright quasars identi ﬁ ed by ground-based surveys at similar redshifts ( e.g., C. J. Willott et al. 2010; L. Jiang et al. 2016; C. Mazzucchelli et al. 2017; Y. Matsuoka et al. 2022; J. Yang et al. 2023 ) and are powered by black…”
A JWST/NIRSpec First Census of Broad-line AGNs at z = 4–7: Detection of 10 Faint AGNs with M BH ∼ 106–108 M ⊙ and Their Host Galaxy Properties (2023, methodology): “…using 4-8 m-class telescopes including the Subaru/Hyper Suprime-Cam survey (Ai-hara et al. 2018) are finding low-luminosity quasars at z ∼ 4 − 7 (e.g., Willott et al. 2010b; Kashikawa et al. 2015; Matsuoka et al. 2016; Onoue et al. 2017; Akiyama et al. 2018; Niida et al. 2020), but these…”
THE LUMINOSITY FUNCTION OF FERMI-DETECTED FLAT-SPECTRUM RADIO QUASARS (2011, background): “The detection of luminous quasars at redshift > 6 (e.g., Fan et al. 2003; Willott et al. 2010) provides evidence of supermassive black hole (SMBH) formation in the ﬁrst 1 Gyr of cosmic time.”
The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, background): “The important issues appear to be whether large numbers of faint quasars exist at high redshift (e.g., Willott et al. 2010; McGreer et al. 2013), whether faint galaxies show an appreciable (>5”
EVIDENCE FOR NON-EVOLVING Fe ii/Mg ii RATIOS IN RAPIDLY ACCRETING z ∼ 6 QSOs (2011, methodology): “Even though the currently faintest known QSOs are included in the study we presented here (Willott et al. 2010a; Kurk et al. 2009), we are still not probing the bulk of QSOs that should be present at that redshift.”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, background): “6.4 (observations collected from several studies: Iwamuro et al. 2002, 2004, Barth et al. 2003, Jiang et al. 2007, Kurk et al. 2007, 2009); Willott et al. (2010b) present data for nine lower luminosity (Lbol < 10 47 erg s−1) z ∼ 6 quasars; finally, Wu et al. (2015) publish an ultra luminous quasar…”
ESCAPE FRACTION OF IONIZING PHOTONS DURING REIONIZATION: EFFECTS DUE TO SUPERNOVA FEEDBACK AND RUNAWAY OB STARS (2014, background): “…to ionizing photons in both the ultraviolet (UV) and X-ray bands but are generally believed to be sub-dominant to stellar sources (Haehnelt et al. 2001; Wyithe & Loeb 2003; Schirber & Bullock 2003; Faucher-Giguère et al. 2008; Cowie et al. 2009; Willott et al. 2010; Fontanot et al. 2014).”
THE BRIGHTEST OF REIONIZING GALAXIES SURVEY: CONSTRAINTS ON THE BRIGHT END OF THE z ∼ 8 LUMINOSITY FUNCTION (2012, neutral): “An exciting, but much less likely, alternative would be a z ∼ 8 QSO, although the limited area of BoRG implies that this occurs with p 5% based on the Willott et al. (2010) QSO LF predictions.”
THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, background): “…Jiang et al. 2006; Fontanot et al. 2007; Bongiorno et al. 2007; Reyes et al. 2008; Jiang et al. 2008, 2009; Croom et al. 2009a; Glikman et al. 2010; Willott et al. 2010; Glikman et al. 2011; Ikeda et al. 2011, 2012; Masters et al. 2012), mid-infrared (Brown et al. 2006; Siana et al. 2008; Assef et…”
Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths (2015, background): “As a consequence, early star-forming galaxies have been favoured as the main drivers of cosmic reionization (e.g. Cowie et al. 2009; Willott et al. 2010; Fontanot et al. 2012), although quasars, mini-quasars and a faint AGN population could also play a significant role (e.g. Volonteri & Gnedin…”
Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6 (2018, methodology): “The derived LF agrees well with the previous results from the SDSS (Jiang et al. 2016) and the CFHQS (Willott et al. 2010) at M1450 < −25 mag, and significantly improves the accuracy at fainter magnitudes.”
Hyper-Eddington accretion flows on to massive black holes (2015, background): “The existence of bright quasars (QSOs) at highredshift (z & 6) provides a challenging puzzle about the origin of supermassive black holes (SMBHs) with masses & 109 M⊙ (Fan 2006; Willott et al. 2010; Mortlock et al. 2011; Venemans et al. 2013; Bañados et al. 2014; Wu et al. 2015).”