Constraining the UV emissivity of AGN throughout cosmic time via X-ray surveys

Abstract

The cosmological process of hydrogen (HI) reionization in the intergalactic medium is thought to be driven by UV photons emitted by star-forming galaxies and ionizing active galactic nuclei (AGN). The contribution of QSOs to HI reionization at $z>4$ has been traditionally believed to be quite modest. However, this view has been recently challenged by new estimates of a higher faint-end UV luminosity function (LF). To set firmer constraints on the emissivity of AGN at $z<6$, we here make use of complete X-ray selected samples including deep Chandra and new COSMOS data, capable to efficiently measure the 1 ryd comoving AGN emissivity up to $z\sim 5-6$ and down to five magnitudes fainter than probed by current optical surveys, without any luminosity extrapolation. We find good agreement between the logN${}_{\mathrm{H}}\lesssim 21-22$ cm${}^{-2}$ X-ray LF and the optically-selected QSO LF at all redshifts for $M_{1450}\le -23$. The full range of the logN${}_{\mathrm{H}}\lesssim 21-22$ cm${}^{-2}$ LF ($M_{1450}\le -17$) was then used to quantify the contribution of AGN to the photon budget critical value needed to keep the Universe ionized. We find that the contribution of ionizing AGN at $z=6$ is as small as 1\% - 7\%, and very unlikely to be greater than 30\%, thus excluding an AGN-dominated reionization scenario.

12 pages, 4 figures, 1 table, submitted to MNRAS after first referee revision

References in corpus (26)

• An Observational Determination of the Bolometric Quasar Luminosity Function
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• The X-ray-to-Optical Properties of Optically-Selected Active Galaxies Over Wide Luminosity and Redshift Ranges
• Model-independent evidence in favor of an end to reionization by z~6
• Absorption Properties and Evolution of Active Galactic Nuclei
• Faint AGNs at z>4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe
• The Direct Detection of Lyman-Continuum Emission from Star-forming Galaxies at z~3
• Obscuration-dependent evolution of Active Galactic Nuclei
• Keeping the Universe ionised: Photo-heating and the clumping factor of the high-redshift intergalactic medium
• Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionisation
• Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
• Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei
• The Subaru high-z quasar survey: discovery of faint z~6 quasars
• High redshift quasars in the COSMOS survey: the space density of z>3 X-ray selected QSOs
• The Photon Underproduction Crisis
• Luminosity Function from dedicated SDSS-III and MMT data of quasars in 0.7<z<4.0 selected with a new approach
• The Hard X-Ray Luminosity Function of High-Redshift ($3<z\lesssim 5$) Active Galactic Nuclei
• Relative Role of Stars and Quasars in Cosmic Reionization
• The deepest X-ray view of high-redshift galaxies: constraints on low-rate black-hole accretion
• The systematic search for $z\gtrsim 5$ active galactic nuclei in the $Chandra$ Deep Field South
• The growth of the nuclear black holes in submillimeter galaxies
• The Chandra COSMOS Legacy survey: the z>3 sample
• The Largest X-ray Selected Sample of z>3 AGNs: C-COSMOS & ChaMP
• High redshift AGNs and HI reionisation: limits from the unresolved X-ray background
• Early-type galaxies in the Chandra COSMOS Survey
• On the Evolution of High-Redshift Active Galactic Nuclei

Cited by in corpus (28)

• High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-$L_{\ast }$ population
• The Far-Ultraviolet Continuum Slope as a Lyman Continuum Escape Estimator at High-redshift
• Optically-Thin Spatially-Resolved Mg II Emission Maps the Escape of Ionizing Photons
• Do galaxies that leak ionizing photons have extreme outflows?
• Supermassive black holes in cosmological simulations II: the AGN population and predictions for upcoming X-ray missions
• Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
• Exploring reionisation and high-z galaxy observables with recent multi-redshift MWA upper limits on the 21-cm signal
• The Lyman Continuum escape fraction of emission line-selected $z\sim 2.5$ galaxies is less than 15%
• BASS XXIV: The BASS DR2 Spectroscopic Line Measurements and AGN Demographics
• The Chandra Deep Fields: Lifting the Veil on Distant Active Galactic Nuclei and X-Ray Emitting Galaxies
• Black hole obscuration and duty cycles mediated by AGN feedback in high redshift galaxies
• The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at $z\sim 2$
• The Pan-STARRS1 $\mathbf{z}>5.6$ Quasar Survey: III. The $\mathbf{z}\approx 6$ Quasar Luminosity Function
• 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 $z\sim 5$
• Modelling a bright z = 6 galaxy at the faint end of the AGN luminosity function
• Aligned metal absorbers and the ultraviolet background at the end of reionization
• Accretion History of AGN III: Radiative Efficiency and AGN Contribution to Reionization
• Outflows in the Gaseous Discs of Active Galaxies and their impact on Black Hole Scaling Relations
• Probing the roles of orientation and multi-scale gas distributions in shaping the obscuration of Active Galactic Nuclei through cosmic time
• Understanding the spatial variation of \ion{Mg}{II} and ionizing photon escape in a local LyC leaker
• MAMBO -- An empirical galaxy and AGN mock catalogue for the exploitation of future surveys
• Euclid preparation. Observational expectations for redshift z<7 active galactic nuclei in the Euclid Wide and Deep surveys
• 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
• Large-scale clustering of buried X-ray AGN: Trends in AGN obscuration and redshift evolution
• The role of scatter and satellites in shaping the large-scale clustering of X-ray AGN as a function of host galaxy stellar mass
• BASS XXX: Distribution Functions of DR2 Eddington-ratios, Black Hole Masses, and X-ray Luminosities
• The impact of black hole feedback on the UV luminosity and stellar mass assembly of high-redshift galaxies