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Arxiv: The impact of faint AGN discovered by JWST on reionization Published: 9/23/2024 9:29:27 PM Updated: 9/23/2024 9:29:27 PM

Paper abstract: The relative contribution of emission from stellar sources and accretion ontosupermassive black holes to reionization has been brought into focus again bythe apparent high abundance of faint AGN at 4<~ z<~11 uncoveredby JWST. We investigate the contribution of these faint AGN to hydrogen and theearly stages of helium reionization using the GPU-based radiative transfer codeATON-HE by post-processing a cosmological hydrodynamical simulation from theSHERWOOD-RELICS suite of simulations. We study four models of reionization: twopreviously studied galaxy-only late-end reionization models and two new models-- a QSO-assisted model and a QSO-only model. In the QSO-assisted model, 1\% ofthe haloes host AGN with a 10~Myr lifetime, and the AGN luminosities are scaledsuch that the AGN contribution to the hydrogen-ionizing emissivity is 20\% ofthat contributed by galaxies. In the QSO-only model, quasars account for allthe hydrogen-ionizing emissivity, with 10\% of the haloes hosting AGN, eachwith a 10 Myr lifetime. All models are calibrated to the observed meanLyman-\alpha forest transmission at 5<~ z<~6.2. We find thatthe QSO-assisted model requires an emissivity factor of 1.8 lower than thegalaxy-only models towards the end of reionization and fits the observeddistribution of the Lyman-\alpha optical depths well. Our QSO-only model isinconsistent with the observed Lyman-\alpha optical depths distribution. Italso results in too high IGM temperatures at z<~ 5 due to an earlyonset of HeII reionization unless the escape fraction of HeII-ionizing photonsis assumed to be low. Our results suggest that a modest contribution toreionization by faint AGN is in good agreement with the Lyman-\alpha forestdata. In contrast, a scenario dominated by faint AGN appears difficult toreconcile with these observations.