2025/10/30 by M. Singha, Sangeeta Malhotra, Singha, Mainak +3
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2510.26990
openalex publication_date 2025/10/30 · openalex created_date 2025/11/05 · openalex updated_date 2026/07/28
The origin of the ionizing photons that completed hydrogen reionization remains debated. Using recent JWST and ground-based surveys at 4.5 <= z <= 6.5, we construct a unified rest-UV AGN luminosity function that separates unobscured Type I and obscured Type II populations, and show that "little red dots" and X-ray selected sources are magnitude-filtered subsets of Type I with a mixture fraction eta = 0.10 +/- 0.02. We anchor the Lyman-continuum (LyC) escape fraction to outflow incidence and geometric clearing rather than assuming quasar-like values for all classes, and propagate uncertainties through a joint fit. Integrating over -27 < MUV < -17, AGN inject Ndotion,AGN = (3.77 +1.08/-0.95) x 1051 s-1 Mpc-3, nearly twice earlier estimates and comparable to the Ly-alpha inferred requirement at z ~ 6. When combined with the JWST galaxy UV luminosity function and a harder stellar ionizing efficiency of log10(xiion) = 25.7, AGN contribute 31-75% of the total ionizing photons for representative galaxy escape fractions fesc,gal = 0.03-0.20. The resulting hydrogen photoionization rate, GammaHI ~ (0.5-2) x 10-12 s-1 at z ~ 5-6, lies squarely within the Ly-alpha forest constraints once mean free paths and IGM clumpiness are accounted for, remaining consistent for combined AGN-galaxy models up to fesc,gal <= 5%. These results suggest that AGN and galaxies jointly sustained the ionizing background during the final stages of reionization, with AGN remaining a major but not exclusive contributor.