James Webb Space Telescope Feed Post

Arxiv: Cosmic Reionization in the JWST Era: Back to AGNs? Published: 6/26/2024 9:59:47 PM Updated: 7/30/2024 1:18:17 AM

Paper abstract: Deep surveys with the James Webb Space Telescope (JWST) have revealed anemergent population of moderate-luminosity, broad-line active galactic nuclei(AGNs) at 4< z< 14 powered by accretion onto early massive black holes. Thehigh number densities reported, together with the large Lyman-continuum (LyC)production efficiency and leakiness into the intergalactic medium (IGM) thatare typical of UV-selected AGNs, lead us to reassess a scenario where AGNs arethe sole drivers of the cosmic hydrogen/helium reionization process. Ourapproach is based on the assumptions, grounded in recent observations, that:(a) the fraction of broad-line AGNs among galaxies is around 10-15%; (b) themean escape fraction of hydrogen LyC radiation is high, >80%, in AGN hosts andis negligible otherwise; and (c) internal absorption at 4 ryd or a steepionizing EUV spectrum delay full reionization of HeII until z~2.8-3.0, inagreement with observations of the HeII Lyman-alpha forest. In our fiducialmodels: 1) hydrogen reionization is 99% completed by redshift z~5.3-5.5, andreaches its midpoint at z~6.5-6.7; (2) the integrated Thomson scatteringoptical depth to reionization is ~0.05, consistent with constraints from cosmicmicrowave background (CMB) anisotropy data; and (3) the abundant AGN populationdetected by JWST does not violate constraints on the unresolved X-raybackground.