The contribution of faint AGNs to the ionizing background at z~4

Abstract

Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in cosmology. Bright QSOs are known to ionize their surrounding neighborhood, but they are too few to ensure the required HI ionizing background. A significant contribution by faint AGNs, however, could solve the problem, as recently advocated on the basis of a relatively large space density of faint active nuclei at z>4. We have carried out an exploratory spectroscopic program to measure the HI ionizing emission of 16 faint AGNs spanning a broad U-I color interval, with I~21-23 and 3.6<z<4.2. These AGNs are three magnitudes fainter than the typical SDSS QSOs (M1450<~-26) which are known to ionize their surrounding IGM at z>~4. The LyC escape fraction has been detected with S/N ratio of ~10-120 and is between 44 and 100% for all the observed faint AGNs, with a mean value of 74% at 3.6<z<4.2 and -25.1<M1450<-23.3, in agreement with the value found in the literature for much brighter QSOs (M1450<~-26) at the same redshifts. The LyC escape fraction of our faint AGNs does not show any dependence on the absolute luminosities or on the observed U-I colors. Assuming that the LyC escape fraction remains close to ~75% down to M1450~-18, we find that the AGN population can provide between 16 and 73% (depending on the adopted luminosity function) of the whole ionizing UV background at z~4, measured through the Lyman forest. This contribution increases to 25-100% if other determinations of the ionizing UV background are adopted. Extrapolating these results to z~5-7, there are possible indications that bright QSOs and faint AGNs can provide a significant contribution to the reionization of the Universe, if their space density is high at M1450~-23.

arXiv commentAccepted for publication on A&A, 16 pages, 22 figures

References in corpus (96)

• The Seventh Data Release of the Sloan Digital Sky Survey
• The Baryon Oscillation Spectroscopic Survey of SDSS-III
• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Radiative transfer in a clumpy universe: IV. New synthesis models of the cosmic UV/X-ray background
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• The Evolution of the Galaxy Rest-Frame Ultraviolet Luminosity Function Over the First Two Billion Years
• Luminosity-dependent evolution of soft X-ray selected AGN: New Chandra and XMM-Newton surveys
• The Chandra COSMOS Legacy survey: overview and point source catalog
• An updated analytic model for the attenuation by the intergalactic medium
• Evidence of patchy hydrogen reionization from an extreme Ly$\alpha$ trough below redshift six
• High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data IV: Luminosity Function from the Fall Equatorial Stripe Sampl
• Planck intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth
• Directly Observing the Galaxies Likely Responsible for Reionization
• Cosmic Reionization after Planck: Could Quasars Do It All?
• Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies
• The Chandra COSMOS Legacy survey: optical/IR identifications
• Detection of Extended He II Reionization in the Temperature Evolution of the Intergalactic Medium
• The Great Observatories Origins Deep Survey. VLT/FORS2 Spectroscopy in the GOODS-South Field: Part III
• New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization
• Faint AGNs at z>4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe
• Full-Data Results of Hubble Frontier Fields: UV Luminosity Functions at $z\sim 6-10$ and a Consistent Picture of Cosmic Reionization
• Lyman continuum leaking from the compact star-forming dwarf galaxy J0925+1403
• The Sloan Digital Sky Survey quasar catalog: tenth data release
• The z~6 Luminosity Function Fainter than -15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties
• Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity
• The tight relation between X-ray and ultraviolet luminosity of quasars
• A strong redshift dependence of the broad absorption line quasar fraction
• The Lyman-Continuum Photon Production Efficiency xi_{ion} of z~4-5 Galaxies from IRAC-based Halpha Measurements: Implications for the Escape Fraction and Cosmic Reionization
• CANDELS: The Contribution of the Observed Galaxy Population to Cosmic Reionization
• The Lyman-alpha forest opacity and the metagalactic hydrogen ionization rate at z~2-4
• The Blast Wave Model for AGN Feedback: Effects on AGN Obscuration
• The Giant Gemini GMOS survey of z>4.4 quasars - I. Measuring the mean free path across cosmic time
• A Local Clue to the Reionization of the Universe
• Hubble imaging of the ionizing radiation from a star-forming galaxy at z=3.2 with fesc>50%
• An extreme [OIII] emitter at $z=3.2$: a low metallicity Lyman continuum source
• The VVDS data reduction pipeline: introducing VIPGI, the VIMOS Interactive Pipeline and Graphical Interface
• Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect
• Escape of Lyman continuum radiation from local galaxies - Detection of leakage from the young starburst Tol 1247-232
• Size--luminosity relations and UV luminosity functions at $z=6-9$ simultaneously derived from the complete Hubble Frontier Fields data
• Q1549-C25: A Clean Source of Lyman-Continuum Emission at $z=3.15$
• No evidence for a significant AGN contribution to cosmic hydrogen reionization
• The Great Observatories Origins Deep Survey: Constraints on the Lyman Continuum Escape Fraction Distribution of Lyman--Break Galaxies at 3.4<z<4.5
• A Measurement of Small Scale Structure in the 2.2 < z < 4.2 Lyman-alpha Forest
• HST-COS Observations of AGN. I. Ultraviolet Composite Spectra of the Ionizing Continuum and Emission Lines
• Direct Detection of Lyman Continuum Escape from Local Starburst Galaxies with the Cosmic Origins Spectrograph
• A Direct Measurement of the IGM Opacity to HI Ionizing Photons
• Large Fluctuations in the High-Redshift Metagalactic Ionizing Background
• The Faint End of the Quasar Luminosity Function at z~4: Implications for Ionization of the Intergalactic Medium and Cosmic Downsizing
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 Quasars and Luminous Galaxies at 5.7 < z < 6.8
• HST-COS Observations of AGN. II. Extended Survey of Ultraviolet Composite Spectra from 159 Active Galactic Nuclei
• Near-zone sizes and the rest frame extreme ultra-violet spectral index of the highest redshift quasars
• The redshift evolution of escape fraction of hydrogen ionizing photons from galaxies
• SDSS-IV MaNGA: Evidence of the importance of AGN feedback in low-mass galaxies
• Measuring the Sources of the Intergalactic Ionizing Flux
• A Deep Hubble and Keck Search for Definitive Identification of Lyman Continuum Emitters at z~3.1
• Early and Extended Helium Reionization Over More Than 600 Million Years of Cosmic Time
• Large scale opacity fluctuations in the Lyman alpha forest: evidence for QSOs dominating the ionising UV background at z ~ 5.5-6 ?
• The Lyman Continuum escape fraction of galaxies at z=3.3 in the VUDS-LBC/COSMOS field
• The Quasar Luminosity Function at Redshift 4 with Hyper Suprime-Cam Wide Survey
• The MUSE Hubble Ultra Deep Field Survey VI: The Faint-End of the Lya Luminosity Function at 2.91 < z < 6.64 and Implications for Reionisation
• On the relative Contribution of high-redshift Galaxies and Active Galactic Nuclei to Reionization
• The Lyman Continuum escape fraction of faint galaxies at z~3.3 in the CANDELS/GOODS-North, EGS, and COSMOS fields with LBC
• Reducing low signal-to-noise FUSE spectra: confirmation of Lyman continuum escape from Haro 11
• The H I opacity of the intergalactic medium at redshifts 1.6 < z < 3.2
• On the Contribution of Active Galactic Nuclei to the High-Redshift Metagalactic Ionizing Background
• The intergalactic medium thermal history at redshift z=1.7--3.2 from the Lyman alpha forest: a comparison of measurements using wavelets and the flux distribution
• Narrowband Lyman-Continuum Imaging of Galaxies at z ~ 2.85
• Constraining the contribution of active galactic nuclei to reionisation
• AGN feedback in dwarf galaxies?
• A Spectroscopic Search for Leaking Lyman Continuum at z~0.7
• The Lyman Continuum Escape Fraction of Low-Mass Star-Forming Galaxies at z~1
• Constraining the UV emissivity of AGN throughout cosmic time via X-ray surveys
• Faint AGN and the Ionizing Background
• The Grism Lens-Amplified Survey from Space (GLASS). III. A census of Lyα Emission at $z\gtrsim$7 from HST Spectroscopy
• AGN feedback at z~2 and the mutual evolution of active and inactive galaxies
• Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
• The Spectral Slope and Escape Fraction of Bright Quasars at $z\sim 3.8$: the Contribution to the Cosmic UV Background
• The Lyman Continuum Escape Fraction of The Cosmic Horseshoe: A Test of Indirect Estimates
• The Lyman Continuum escape fraction of emission line-selected $z\sim 2.5$ galaxies is less than 15%
• New constraints on the average escape fraction of Lyman continuum radiation in z~4 galaxies from the VIMOS Ultra Deep Survey (VUDS)
• Constraints on the Lyman continuum escape fraction for faint star forming galaxies
• A New Method to Measure the Post-Reionization Ionizing Background from the Joint Distribution of Lyman-$\alpha$ and Lyman-$\beta$ Forest Transmission
• Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey
• Cosmic Reionization After Planck and Before JWST: An Analytic Approach
• Limits on the LyC signal from z~3 sources with secure redshift and HST coverage in the E-CDFS field
• The Lyman Continuum Escape and ISM properties in Tololo 1247-232 - New Insights from HST and VLA
• AGN-enhanced outflows of low-ionization gas in star-forming galaxies at 1.7<z<4.6
• Lyman continuum leaking AGN in the SSA22 field
• Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies
• Ultra-Luminous X-ray Sources in Haro 11 and the Role of X-ray Binaries in Feedback in Lyman-alpha Emitting Galaxies
• Easylife: the data reduction and survey handling system for VIPERS
• Hard X-ray selected AGNs in low-mass galaxies from the NuSTAR serendipitous survey
• AGNs as main contributors to the UV ionizing emissivity at high redshifts: predictions from a Lambda-CDM model with linked AGN/galaxy evolution
• A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255 II. Emission- and absorption-line variability time lags
• Resolving the X-ray emission from the Lyman continuum emitting galaxy Tol 1247-232

Cited by in corpus (43)

• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Evolution of the AGN UV luminosity function from redshift 7.5
• Galaxy Formation and Reionization: Key Unknowns and Expected Breakthroughs by the James Webb Space Telescope
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6
• New synthesis models of consistent extragalactic background light over cosmic time
• Reionization with galaxies and active galactic nuclei
• The Obelisk simulation: galaxies contribute more than AGN to HI reionization of protoclusters
• Reionization in Technicolor
• Witnessing the onset of reionisation via Lyman-$\alpha$ emission at redshift 13
• No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $3.1\lesssim \mathbf{z}\lesssim 3.5$
• Spectroscopically Confirmed Lyman-Alpha Emitters from Redshift 5 to 7 Behind Ten Galaxy Cluster Lenses
• Observational constraints on key-parameters of cosmic reionisation history
• 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 Lyman Continuum Escape Fraction of Galaxies and AGN in the GOODS Fields
• 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
• A high space density of L* Active Galactic Nuclei at z~4 in the COSMOS field
• The spectroscopic follow-up of the QUBRICS bright quasar survey
• 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
• UNCOVERing the contribution of black holes to reionization in the JWST era
• Modelling a bright z = 6 galaxy at the faint end of the AGN luminosity function
• Nature and chemical abundances of a sample of Lyman-$\alpha$ emitter objects at high redshift
• Outside the Lyman-break box: detecting Lyman continuum emitters at $3.5<z<5.1$ with CLAUDS
• Astraeus VI: Hierarchical assembly of AGN and their large-scale effect during the Epoch of Reionization
• Accretion History of AGN III: Radiative Efficiency and AGN Contribution to Reionization
• CHORUS. I. Cosmic HydrOgen Reionization Unveiled with Subaru: Overview
• The Infrared Medium-deep Survey. \Romannum{7}. Faint Quasars at $z\sim 5$ in the ELAIS-N1 Field
• 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)
• The role of AGN jets in the reionization epoch
• Evolution of the Lyman-α emitting fraction and UV properties of lensed star-forming galaxies between 2.9 < z < 6.7
• Subaru narrow-band imaging search for Lyman continuum from galaxies at z>3 in the GOODS-N field
• Eddington accreting Black Holes in the Epoch of Reionization
• AGN jets versus accretion as reionization sources
• The impact of faint AGN discovered by JWST on reionization
• AGN ruled out as the dominant source of cosmic reionization
• A Cautionary Tale of LyC Escape Fraction Estimates from High Redshift Galaxies
• Observations of Ly$\alpha$ Emitters at High Redshift
• Spectroscopy of an extreme [OIII] emitting active galactic nucleus at $z=3.212$: implications for the reionisation era
• The Ly$\alpha$ and Continuum Origins Survey. III. Investigating the Link between Galaxy Morphology, Merger Properties and LyC Escape
• Emission Line Galaxies in the SHARDS Hubble Frontier Fields II: Limits on Lyman-Continuum Escape Fractions of Lensed Emission Line Galaxies at Redshifts 2 < z < 3.5
• The impact of cosmic ray feedback during the epoch of reionisation
• The CUBES Science Case
• The impact of black hole feedback on the UV luminosity and stellar mass assembly of high-redshift galaxies