James Webb Space Telescope Feed Post

Harvard ADS: Ionising properties of galaxies in JADES for a stellar mass complete sample: resolving the cosmic ionising photon budget crisis at the Epoch of Reionisation

Paper abstract: We use NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the ionising properties of a sample of 14652 galaxies at 3 = z_phot = 9, 90% complete in stellar mass down to log(M_?/[M_?]) ˜ 7.5. Out of the full sample, 1620 of the galaxies have spectroscopic redshift measurements from the literature. We use the spectral energy distribution fitting code Prospector to fit all available photometry and infer galaxy properties. We find a significantly milder evolution of the ionising photon production efficiency (?_ion) with redshift and UV magnitude than previously reported. Interestingly, we observe two distinct populations in ?_ion, distinguished by their burstiness (given by SFR₁₀/SFR₁₀₀). Both populations show the same evolution with z and M_UV, but have a different ?_ion normalisation. We convolve the more representative log (?_ion(z, M_UV)) relations (accounting for ~97% of the sample), with luminosity functions from literature, to place constraints on the cosmic ionising photon budget. By combining our results, we find that one of our models can match the observational constraints from the Lya forest at z ? 6. We conclude that galaxies with M_UV between -16 and -20, adopting a reasonable escape fraction, can produce enough ionising photons to ionise the Universe, without exceeding the required ionising photon budget.