The ionizing photon budget and effective clumping factor in radiative transfer simulations calibrated to Lyman-α forest data

ABSTRACT Recent JWST observations have allowed for the first time to obtain comprehensive measurements of the ionizing photon production efficiency $\xi _\text{ion}$ for a wide range of reionization-epoch galaxies. We explore implications for the inferred UV luminosity functions and escape fractions of ionizing sources in our suite of simulations. These are run with the graphics processing unit (GPU) based radiative transfer code aton-he and are calibrated to the XQR-30 Lyman-$\alpha$ forest data at $5< z < 6.2$. For our fiducial source model, the inferred ionizing escape fractions increase from (6.1, 5.4, 4.9) per cent at $z=6$ to (14.4, 23.8, 29.4) per cent at $z=10$ for our (Fiducial, Early, Extremely Early) models in good agreement with extrapolations of lower redshift escape fraction measurements. Extrapolating observed luminosity functions beyond the resolution limit of the simulations to faint sources with $M_\text{UV}=-11$ increases the inferred escape fractions by a factor ${\sim} 1.5$ at $z=10$. For our oligarchic source model, where no ionizing photons are emitted in faint sources, the inferred escape fractions increase from 10 per cent at $z=6$ to uncomfortably large values ${>}50$ per cent at $z> 10$, disfavouring the oligarchic source model at very high redshift. The inferred effective clumping factors in our simulations are in the range of $3{\!-\!}6$, suggesting consistency between the observed ionizing properties of reionization-epoch galaxies and the ionizing photon budget in our simulations.