A Survey of z > 5.8 Quasars in the Sloan Digital Sky Survey. I. Discovery of Three New Quasars and the Spatial Density of Luminous Quasars at z ∼ 6

By Xiaohui Fan, V. Narayanan, Robert Lupton, M. Strauss, G. Knapp, Robert H. Becker, R. White, L. Pentericci, S. Leggett, Zoltán Haiman and 24 more. 2001

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We present the results from a survey of i-dropout objects selected from ∼1550 deg2 of multicolor imaging data from the Sloan Digital Sky Survey to search for luminous quasars at z ≳ 5.8. Objects with i*-z* > 2.2 and z* < 20.2 are selected, and follow-up J-band photometry is used to separate L- and T-type cool dwarfs from high-redshift quasars. We describe the discovery of three new quasars, SDSSp J083643.85+005453.3 (z = 5.82), J130608.26+035626.3 (z = 5.99), and J103027.10+052455.0 (z = 6.28). The quasar SDSSp J083643.85+005453.3 is a radio source with flux of 1.1 mJy at 20 cm. The spectra of all three quasars show strong and broad Lyα + N V emission lines and very strong Lyα forest absorption, with a mean continuum decrement DA > 0.90. The ARC 3.5 m spectrum of SDSSp J103027.10+052455.0 shows that over a range of ∼300 Å immediately blueward of the Lyα emission, the average transmitted flux is only 0.003 ± 0.020 times that of the continuum level, consistent with zero flux over a ∼300 Å range of the Lyα forest region and suggesting a tentative detection of the complete Gunn-Peterson trough. The existence of strong metal lines in the quasar spectra suggests early metal enrichment in the quasar environment. The three new objects, together with the previously published z = 5.8 quasar SDSSp J104433.04-012502.2, form a complete color-selected flux-limited sample at z ≳ 5.8. We estimate the selection function of this sample, taking into account the estimated variations in the quasar spectral energy distribution, as well as observational photometric errors. We find that at z = 6, the comoving density of luminous quasars at M1450 < -26.8 (H0 = 50 km s-1 Mpc-1, Ω = 1) is 1.1 × 10-9 Mpc-3. This is a factor of ∼2 lower than that at z ∼ 5 and is consistent with an extrapolation of the observed quasar evolution at z < 5. Using the current sample, we discuss the constraint on the shape of the quasar luminosity function and the implications for the contribution of quasars to the ionizing background at z ∼ 6. The luminous quasars discussed in the paper have central black hole masses of several times 109 M⊙ by the Eddington argument, with likely dark halo masses on the order of 1013 M⊙. Their observed space density provides a sensitive test of models of quasar and galaxy formation at high redshift.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “However, observations of the Gunn & Peterson (1965) trough in quasar spectra (e.g., Fan et al. 2001, 2002, 2003, 2006b; Djorgovski et al. 2001) indicate that intergalactic gas hasbecome almost fully reionized by redshiftz ∼ 5.”
CONSTRAINTS ON BLACK HOLE GROWTH, QUASAR LIFETIMES, AND EDDINGTON RATIO DISTRIBUTIONS FROM THE SDSS BROAD-LINE QUASAR BLACK HOLE MASS FUNCTION (2010, background): “At high-redshift SMBHs with masses MBH ∼ 109 are already in place by z ∼ 6 (e.g., Fan et al. 2001b; Jiang et al. 2007), and therefore the high-z BLQSO BHMF places important constraints on the formation and growth of seed SMBHs (e.g., Volonteri et al. 2003, 2008; Lodato & Natarajan 2007).”
Formation of supermassive black holes (2010, background): “At the other end, however, some powerful quasars have already been detected at z > 6, corresponding to a time less than a tenth of the age of the Universe, roughly one billion years after the Big Bang.”
Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity (2004, methodology): “Objects this red are rare; at the SDSS magnitude limits they are late L and T dwarfs, quasars at redshift greater than 5.7 (Fan et al. 2001, 2003) or very rare unusual broad absorption line quasars (see Hall et al. 2002), and their surface density is smaller than about one per 50 deg2.”
Unusual Broad Absorption Line Quasars from the Sloan Digital Sky Survey (2002, background): “SDSS 0819+4209 SDSS 0819+4209 (Figure 8a) was discovered in a search for z & 5.8 quasars among i-dropouts in SDSS images (Fan et al. 2001).”
Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars (2005, methodology): “In a series of papers (Fan et al. 2000, 2001, 2003, 2004, 2006), we have reported the selection and identification of nineteen quasars selected from about 6600 deg2 of SDSS imaging.”
The global 21-centimeter background from high redshifts (2006, background): “The rapid evolution of the mean Lyα optical depth in quasar absorption spectra seems to indicate that reionization is ending at z ∼ 6 (Fan et al. 2001, 2006).”
The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function (2004, background): “The increasing number of high redshift QSOs from the SDSS survey (Fan et al. 2001) may remedy this situation.”
MASS FUNCTIONS OF THE ACTIVE BLACK HOLES IN DISTANT QUASARS FROM THE LARGE BRIGHT QUASAR SURVEY, THE BRIGHT QUASAR SURVEY, AND THE COLOR-SELECTED SAMPLE OF THE SDSS FALL EQUATORIAL STRIPE (2009, methodology): “This is also consistent with the observed rise in the quasar space density at these redshifts (e.g., Osmer 1982; Schmidt et al. 1995; Warren et al. 1994; Fan et al. 2001b) and the relatively high Eddington luminosity ratios observed for the SDSS color-selected sample (Fig.”
Inferences on the timeline of reionization at z ∼ 8 from the KMOS Lens-Amplified Spectroscopic Survey (2019, background): “Measurements of the reionization timeline are challenging, however, due to the rarity of bright quasars at z > 6 (Fan et al. 2001; Manti et al. 2016; Parsa et al. 2018), which have historically provided strong constraints on the end stages of reionization (e.g., Fan et al. 2006; McGreer et al.…”
Observational evidence for intermediate-mass black holes (2017, neutral): “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).”
Sloan Digital Sky Survey: Early Data Release (2002, background): “This is particularly problematic in z, where the occasional cosmic ray can splatter in the thick chip to be indistinguishable from the PSF (see the discussion in Fan et al. 2001a).”
Escape fraction of ionizing photons from high-redshift galaxies in cosmological SPH simulations (2010, methodology): “Using the SDSS sample, Fan et al. (2001) showed that the bright-end slope of the quasar luminosity function at z >∼ 4 are considerably steeper than that at lower redshifts, and concluded that the quasars cannot maintain the ionization of IGM at z >∼ 4.”
Low-Frequency Gravitational Waves from Massive Black Hole Binaries: Predictions for LISA and Pulsar Timing Arrays (2002, background): “Recent observations of this population have reached out beyond redshift 6 (Fan et al. 2001).”
The Direct Detection of Lyman Continuum Emission from Star-forming Galaxies at z~3 (2006, background): “…important ingredient of the ionizing background at redshifts beyond z ∼ 3, and may dominate the radiation field at the epoch of H I reionization (Fan et al. 2001; Spergel et al. 2003), estimating the galaxy contribution directly represents a fundamental goal for observational cosmology.”
Reionization of Hydrogen and Helium by Early Stars and Quasars (2002, methodology): “This quasar evolution model successfully describes all known properties of the high-redshift quasar luminosity function (Fan et al. 2001a, 2001b) and reproduces measurements of the black hole/dark matter halo mass relation (Ferrarese 2002) as well as estimates of the quasar duty cycle (Steidel et…”
Evolution of the Ionizing Background and the Epoch of Reionization from the Spectra of z ∼ 6 Quasars (2001, methodology): “If the universe was ionized by luminous quasars (unlikely based on current statistical on quasar evolution, Fan et al. 2001c), the large HII regions produced by them near the epoch of overlap could even lead to gaps in transmitted flux (Haiman & Loeb 1998, Miralda-Escudé et al. 2000).”