在 JWST 时代探索活动星系核对宇宙再电离的贡献
Revisiting the AGN contribution to reionization in JWST era
The Epoch of Reionization (EoR) is one of the major cosmic phase transitions, when the Lyman continuum (LyC) photons turned the Universe from neutral to highly ionized. The major sources of LyC photons at the EoR have been long debated.
High-redshift galaxies and quasars (also referring to active galactic nuclei, hereafter AGNs) are thought to be two plausible candidates, with unclear individual contributions. Owing to the intergalactic medium absorption, the contribution of high-redshift galaxies is unconstrained. The average escape fraction of LyC photons from galaxies is small and uncertain at high redshift. Instead, quasars are known to have higher escape fraction, close to unity. Previous studies of bright quasars indicate that their low number density at high redshift results in a negligible role in reionization. Recently, JWST observations reveal numerous faint AGNs, in excess of a hundred times compared to previously expected. In this talk, I will review previous studies on the high-redshift quasar luminosity function and AGN contribution to reionization, as well as the recent discoveries of faint AGNs by JWST. I will also introduce our recent work, which strongly re-constrains the faint end of the AGN UV luminosity function and the role of AGNs in cosmic reionization.
