Late-end reionization with ATON-HE: towards constraints from Lyman-α emitters observed with JWST

We present a new suite of late-end reionization simulations performed with ATON-HE, a revised version of the GPU-based radiative transfer code ATON that includes helium. The simulations are able to reproduce the Lyα flux distribution of the E-XQR-30 sample of QSO absorption spectra at 5 ≲ z ≲ 6.2, and show that a large variety of reionization models are consistent with these data. We explore a range of variations in source models and in the early-stage evolution of reionization. Our fiducial reionization history has a midpoint of reionization at z = 6.5, but we also explore an `Early' reionization history with a midpoint at z = 7.5 and an `Extremely Early' reionization history with a midpoint at z = 9.5. Haloes massive enough to host observed Lyα emitters are highly biased. The fraction of such haloes embedded in ionized bubbles that are large enough to allow high Lyα transmission becomes close to unity much before the volume filling factor of ionized regions. For our fiducial reionization history this happens at z = 8, probably too late to be consistent with the detection by JWST of abundant Lyα emission out to z = 11. A reionization history in our `Early' model or perhaps even our `Extremely Early' model may be required, suggesting a Thomson scattering optical depth in tension with that reported by Planck, but consistent with recent suggestions of a significantly higher value.