Revised AGN Spectral Model Reveals a More Significant Role in Cosmic Reionization

TL;DR

This study uses an improved AGN spectral model combined with observations to show that AGNs likely contributed more significantly to cosmic reionization than previously thought, potentially accounting for around 20% of the process.

Contribution

The paper introduces a more sophisticated AGN spectral energy distribution model and demonstrates its impact on the estimated contribution of AGNs to cosmic reionization.

Findings

AGN contribution to reionization increased by a factor of 3-4 with the new model.

Faint AGNs further boost the ionizing photon output.

Results are consistent across various accretion rates and escape fractions.

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 (AGNs) 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 AGNs 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$\sim$4, elevating AGNs to a more significant role ($\approx$20\%) in maintaining reionization than previously estimated. The inclusion of abundant faint AGNs 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 AGNs may have played a more prominent and previously underestimated role in the reionization of the Universe.