UNCOVERing the contribution of black holes to reionization in the JWST era

Abstract

With its sensitivity in the rest-frame optical, the James Webb Space Telescope (JWST) has uncovered active galactic nuclei (AGN), comprising both intrinsically faint and heavily reddened sources, well into the first billion years of the Universe, at $z\sim 4-11$. In this work, we revisit the AGN contribution to reionization given the high number densities associated with these objects. We use the DELPHI semi-analytic model, base-lined against the latest high-redshift datasets from the JWST and the Atacama Large millimetre Array (ALMA) to model early star forming galaxies and AGN. We calculate the escape fractions of ionizing radiation from both star formation and AGN and include the impact of reionization feeback in suppressing the baryonic content of low-mass galaxies in ionized regions. This model is validated against the key observables for star forming galaxy, AGN and reionization. In our {\it fiducial} model, reionization reaches its mid-point at $z\sim 6.9$ and ends by $z\sim 5.9$. Low stellar mass ($M_{\ast }\le 10^9{M}_{\odot }$) star forming galaxies are found to be the key drivers of the reionization process, providing about $77\%$ of the total photon budget. Despite their high numbers, high accretion rates and higher escape fractions compared to star forming galaxies at $z\sim 5$, AGN only provide about $23\%$ of the total reionization budget which is dominated by black holes in high stellar mass systems (with $M_{\ast }\ge 10^9{M}_{\odot }$). This is because AGN number densities become relevant only at $z\le 7$ - as a result, AGN contribute as much as galaxies as late as $z\sim 6.2$, when reionization is already in its end stages. Finally, we find that even contrasting models of the AGN ionizing photon escape fraction (increasing or decreasing with stellar mass) do not qualitatively change our results.

Accepted to A&A

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Cited by in corpus (15)

• The Dual Nature of GHZ9: Coexisting Active Galactic Nuclei and Star Formation Activity in a Remote X-ray Source at z = 10.145
• Synergising semi-analytical models and hydrodynamical simulations to interpret JWST data from the first billion years
• JADES reveals a large population of low mass black holes at high redshift
• The properties of primordially-seeded black holes and their hosts in the first billion years: implications for JWST
• Little impact of mergers and galaxy morphology on the production and escape of ionizing photons in the early Universe
• AGN ruled out as the dominant source of cosmic reionization
• Probing Reionization-Era Galaxies with JWST UV Luminosity Functions and Large-Scale Clustering
• High-redshift AGN population in radiation-hydrodynamics simulations
• The impact of cosmic ray feedback during the epoch of reionisation
• REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization
• ECHO21: a tool for modelling global 21-cm signal from dark ages to reionization
• Double-Peaked Ly$\alpha$ Emission during Reionization Requires Nearby Voids and a Favorable Local Ionizing Background
• A Lyman continuum analysis for $\sim 100$ galaxies at $z_{\text{spec}}\sim 3$ in the Abell 2744 Cluster Field
• Estimating the completeness of the QUBRICS Survey with 3501 QSO redshifts from Gaia DR3 spectra
• Black Hole merger rates in the first billion years in light of JWST data