Dr Aayush Saxena

Abstract:

JWST observations are providing unprecedented constraints on the history of reionization owing to the ability to detect faint galaxies at z ≫ 6. Modelling this history requires understanding both the ionizing photon production rate (ξion) and the fraction of those photons that escape into the intergalactic medium (fesc). Observational estimates of these quantities generally rely on spectroscopy for which large samples with well-defined selection functions remain limited. To overcome this challenge, we present and release a novel implicit likelihood inference pipeline, PHOTONIOn, trained on mock photometry to predict the escaped ionizing luminosity of individual galaxies (N ion) based on photometric magnitudes and redshifts. We show that PHOTONIOn is able to reliably infer N ion from photometry. This is in contrast to traditional spectral energy distribution-fitting approaches which rely on fesc prescriptions that often overpredict N ion for Lyman Continuum (LyC)-dim galaxies, even when given access to spectroscopic data. We have deployed PHOTONIOn on a sample of 4559 high-redshift galaxies from the JWST Advanced Deep Extragalactic Survey (JADES), finding gentle redshift evolutions of log10(N ion) = (0.08 ± 0.01)z + (51.60 ± 0.06) and log10(fescξion) = (0.07 ± 0.01)z + (24.12 ± 0.07). Late-time values for the ionizing photon production rate density are consistent with both theoretical models and observations. Finally, we measure the evolution of the intergalactic medium ionized fraction to find that observed populations of star-forming galaxies are capable of driving reionization in this field to completion by z ∼ 5.3 without the need for active galactic nucleus or other exotic sources, consistent with other studies of the same field. The 20 per cent of UV-brightest galaxies (MUV < −18.5) reionize roughly 35 per cent of the survey volume, demonstrating that UV faint LyC emitters are crucial for reionization.