Revised Active Galactic Nuclei Spectral Model Reveals a More Significant Role in Cosmic Reionization

Abstract Reionization marks one of the most important phase transitions in the history of the Universe, during which neutral baryonic matter was transformed into ionized plasma. While star-forming galaxies are widely regarded as the primary drivers of this process, the extent to which active galactic nuclei (AGN) contribute remains a subject of ongoing investigation. In this study, we integrate a physically motivated AGN spectral energy distribution (SED) model with state-of-the-art observations to reassess the contribution of AGN to cosmic reionization. Our findings indicate that adopting a more sophisticated AGN SED model could substantially increase the predicted ionizing photon output by a factor of 3 ∼ 4, elevating AGN to a more significant role (≈20%) in maintaining reionization than previously estimated. The inclusion of abundant faint AGN further amplifies this contribution by a factor of a few. These conclusions remain robust across a wide range of accretion rates and ionizing photon escape fractions. Collectively, our results suggest that AGN may have played a more prominent and previously underestimated role in the reionization of the Universe.