The Incidence of Large Ionized Bubbles at Redshift 13

Ionized bubbles around the first galaxies link early galaxy growth, ionizing photon escape, intergalactic-medium topology, Ly alpha visibility, 21 cm structure, and the timing of reionization. With JWST now constraining both the abundance of luminous galaxies at z 10 and rare Ly alpha emitters deep in the neutral era, it is timely to ask how often galaxy populations produce large ionized environments. We model the incidence of galaxy-driven ionized bubbles at z about 13 using JWST UV luminosity functions, taking the Ly alpha source reported by Witstok et al. (2025) as a benchmark for the relevant bubble scale. We quantify the incidence of regions with comoving radius R 2.5 cMpc through the sky surface density 2.5 at z about 13. For our fiducial case (UVLF from Donnan et al. 2024 with f esc=0.2, xi ion=25.5, f duty=1, and C=3), we find 2.5 1.33 times 10-2 arcmin-2 per z=1. Because bubbles are treated as independent spheres with random source positions and no union of overlaps, this is a conservative baseline for the abundance of connected ionized environments. We conclude that Witstok-sized regions are plausible in UVLF-calibrated galaxy-driven models. This is a population-level statement, however, and the specific Witstok source may still require unusual effective ionizing efficiency, recent fading or burstiness, or a non-stellar ionizing contribution.