The space density of ultra-luminous QSOs at the end of reionization epoch by the QUBRICS Survey and the AGN contribution to the hydrogen ionizing background

Abstract

Motivated by evidences favoring a rapid and late hydrogen reionization process completing at z~5.2-5.5 and mainly driven by rare and luminous sources, we have reassessed the estimate of the space density of ultra-luminous QSOs at z~5 in the framework of the QUBRICS survey. A ~90% complete sample of 14 spectroscopically confirmed QSOs at M1450<-28.3 and 4.5<z<5.0 has been derived in an area of 12,400 sq. deg., thanks to multi-wavelength selection and GAIA astrometry. The space density of z~5 QSOs within -29.3<M1450<-28.3 is three times higher than previous determinations. Our results suggest a steep bright-end slope for the QSO luminosity function at z~5 and a mild redshift evolution of the space density of ultra-bright QSOs (M1450~-28.5) at 3<z<5.5, in agreement with the redshift evolution of the much fainter AGN population at M1450~-23. These findings are consistent with a pure density evolution for the AGN population at z>3. Adopting our z~4 QSO luminosity function and applying a mild density evolution in redshift, a photo-ionization rate of GammaHI=0.46+0.17-0.09x10^-12 s^-1 has been obtained at z=4.75, assuming an escape fraction of ~70% and a steep faint-end slope of the AGN luminosity function. The derived photo-ionization rate is ~50-100% of the ionizing background measured at the end of the reionization epoch, suggesting that AGNs could play an important role in the cosmological reionization process.

Accepted for publication in ApJ. 15 pages, 3 figures, 3 tables

References in corpus (39)

• The Gaia mission
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• Observational constraints on Cosmic Reionization
• New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Faint AGNs at z>4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe
• The Dark Energy Survey Data Release 2
• The first ultraviolet quasar stacked spectrum at z=2.4 from WFC3
• A measurement of secondary cosmic microwave background anisotropies from the 2500-square-degree SPT-SZ survey
• A Survey of z~6 Quasars in the SDSS Deep Stripe: I. a Flux-Limited Sample at z_{AB}<21
• Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5
• CO(1-0) in z >/~ 4 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• An Improved Measurement of the Secondary Cosmic Microwave Background Anisotropies from the SPT-SZ + SPTpol Surveys
• An uncontaminated measurement of the escaping Lyman continuum at $z\sim 3$
• The Subaru high-z quasar survey: discovery of faint z~6 quasars
• A survey of luminous high-redshift quasars with SDSS and WISE II. the bright end of the quasar luminosity function at z ~ 5
• The Evolution of the Lyman-Alpha Luminosity Function During Reionization
• Chasing the Tail of Cosmic Reionization with Dark Gap Statistics in the Ly$\alpha$ Forest over $5<z<6$
• The Faint End of the Quasar Luminosity Function at $z\sim 5$ from the Subaru Hyper Suprime-Cam Survey
• A short mean free path at $z=6$ favors late and rapid reionization by faint galaxies
• The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey footprint. III. The South Galactic Cap Sample and the Quasar Luminosity Function at Cosmic Noon
• The Predicament of Absorption-Dominated Reionization: Increased Demands on Ionizing Sources
• On the AGN nature of two UV bright sources at z_spec~5.5 in the CANDELS fields: an update of the AGN space density at M1450~-22.5
• The Infrared Medium-deep Survey. VIII. Quasar Luminosity Function at $z\sim 5$
• The Lyman continuum escape fraction and the Mean Free Path of hydrogen ionizing photons for bright z~4 QSOs from SDSS DR14
• The spectroscopic follow-up of the QUBRICS bright quasar survey
• The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint (PS-ELQS)
• Random Forests as a viable method to select and discover high redshift quasars
• Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper
• The Luminosity Function of bright QSOs at z~4 and implications for the cosmic ionizing background
• The Probabilistic Random Forest applied to the selection of quasar candidates in the QUBRICS Survey
• Constraining the cosmic UV background at z>3 with MUSE Lyman-α emission observations
• Pure Density Evolution of the Ultraviolet Quasar Luminosity Function at $2\lesssim z\lesssim 6$
• The evolution of the UV luminosity and stellar mass functions of Lyman-alpha emitters from z~2 to z~6
• Ionizing radiation from AGNs at z>3.3 with the Subaru Hyper Suprime-Cam Survey and the CFHT Large Area U-band Deep Survey (CLAUDS)
• Reality or Mirage? Observational Test and Implications for the Claimed Extremely Magnified Quasar at $z=6.3$

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