Definitive upper bound on the negligible contribution of quasars to cosmic reionization

Abstract

Cosmic (hydrogen) reionization marks one of the major phase transitions of the universe at redshift z >= 6. During this epoch, hydrogen atoms in the intergalactic medium (IGM) were ionized by Lyman continuum (LyC) photons. However, it remains challenging to identify the major sources of the LyC photons responsible for reionization. In particular, individual contributions of quasars (or active galactic nuclei, AGNs) and galaxies are still under debate. Here we construct the far-ultraviolet (far-UV) luminosity function for type 1 quasars at z >= 6 that spans 10 magnitudes (-19 < M_UV < -29), conclusively showing that quasars made a negligible contribution to reionization. We mainly search for quasars in the low-luminosity range of M_UV > -23 mag that is critical to determine quasars' total LyC photon production but has been barely explored previously. We find that the quasar population can only provide less than 7% (95% confidence level) of the total photons needed to keep the universe ionized at z = 6.0 - 6.6. Our result suggests that galaxies, presumably low-luminosity star-forming systems, are the major sources of hydrogen reionization.

Published in Nature Astronomy on June 16, 2022; 18 pages; authors' version; publisher's version is here (https://www.nature.com/articles/s41550-022-01708-w)

References in corpus (26)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The Cosmic Evolution Survey (COSMOS) -- Overview
• UltraVISTA: a new ultra-deep near-infrared survey in COSMOS
• The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe
• Third Data Release of the Hyper Suprime-Cam Subaru Strategic Program
• 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
• The first ultraviolet quasar stacked spectrum at z=2.4 from WFC3
• Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• Six more quasars at redshift 6 discovered by the Canada-France High-z Quasar Survey
• Relative Role of Stars and Quasars in Cosmic Reionization
• Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
• Near-Infrared Imaging of a z=6.42 Quasar Host Galaxy With the Hubble Space Telescope Wide Field Camera 3
• No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $3.1\lesssim \mathbf{z}\lesssim 3.5$
• The Magellan M2FS Spectroscopic Survey of High-$z$ Galaxies: Lyα Emitters at $z\approx 6.6$ and the Evolution of Lyα Luminosity Function over $z\approx 5.7-6.6$
• The Predicament of Absorption-Dominated Reionization: Increased Demands on Ionizing Sources
• 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
• A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5<z<6.8: Program Overview and a Sample of the Brightest Lyman-alpha Emitters
• The Magellan M2FS Spectroscopic Survey of High-Redshift Galaxies: A Sample of 260 Ly$\alpha$ Emitters at Redshift $z\approx 5.7$
• High-redshift quasars and their host galaxies II: multiphase gas and stellar kinematics
• 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)
• A Physical Model for the Quasar Luminosity Function Evolution between Cosmic Dawn and High Noon
• The Contribution of AGN Accretion Disks to Hydrogen Reionization

Cited by in corpus (16)

• A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe
• Peering into cosmic reionization: the Ly$\alpha$ visibility evolution from galaxies at $z$ = 4.5-8.5 with JWST
• The Pan-STARRS1 $\mathbf{z}>5.6$ Quasar Survey: III. The $\mathbf{z}\approx 6$ Quasar Luminosity Function
• An Hα Impression of Lyα Galaxies at $z\simeq 6$ with Deep JWST/NIRCam Imaging
• Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec
• A universal average spectral energy distribution for quasars from optical to extreme ultraviolet
• The THESAN project: connecting ionized bubble sizes to their local environments during the Epoch of Reionization
• The Assembly of Black Hole Mass and Luminosity Functions of High-redshift Quasars via Multiple Accretion Episodes
• Ionizing photon production and escape fractions during cosmic reionization in the TNG50 simulation
• Evolution of the Lyman-α emitting fraction and UV properties of lensed star-forming galaxies between 2.9 < z < 6.7
• AGN ruled out as the dominant source of cosmic reionization
• Galaxy Formation and Symbiotic Evolution with the Inter-Galactic Medium in the Age of ELT-ANDES
• The Infrared Medium-deep Survey. IX. Discovery of Two New $z\sim 6$ Quasars and Space Density down to $M_{1450}\sim -23.5$ mag
• The Composite Spectral Energy Distribution of Quasars is Surprisingly Universal Since Cosmic Noon
• Impact of the turnover in the high-z galaxy luminosity function on the 21-cm signal during Cosmic Dawn and Epoch of Reionization
• POLAR-II: modeling star formation history of galaxies on the 21-cm signal from Epoch of Reionization