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Arxiv: Inferring the Ionizing Photon Contributions of High-Redshift Galaxies to Reionization with JWST NIRCam Photometry Published: 5/16/2024 1:30:51 AM Updated: 1/21/2025 1:03:55 PM

Paper abstract: JWST is providing constraints on the history of reionization owing to itsability to detect faint galaxies at z\gg6. Modeling this history requiresunderstanding both the ionizing photon production rate (\xi_{\rm ion}) andthe fraction of those photons that escape into the intergalactic medium(f_{\rm esc}). Observational estimates of these quantities generally rely onspectroscopy for which large samples with well-defined selection functions arelimited. To overcome this challenge, we present and release an implicitlikelihood inference pipeline, PHOTONIOn, trained on mock photometry to predictthe escaped ionizing luminosity of individual galaxies (\dot{N}_{\rm ion})based on photometric magnitudes and redshifts. We show that PHOTONIOn is ableto reliably infer \dot{N}_{\rm ion} from photometry. This is in contrast totraditional SED-fitting approaches which rely on f_{\rm esc} prescriptionsthat often over-predict \dot{N}_{\rm ion} for LyC-dim galaxies, even whengiven access to spectroscopic data. We have deployed PHOTONIOn on a sample of4,559 high-redshift galaxies from the JADES Deep survey, finding gentleredshift evolutions of \log_{10}(\dot{N}_{\rm ion}) = (0.08\pm0.01)z +(51.60\pm0.06) and \log_{10}(f_{\rm esc}\xi_{\rm ion}) = (0.07\pm0.01)z +(24.12\pm0.07). Late-time values for the ionizing photon production ratedensity are consistent with theoretical models and observations. We measure theevolution of the IGM ionized fraction to find that observed populations ofstar-forming galaxies are capable of driving reionization in GOODS-S tocompletion by z~ 5.3 without the need for AGN or other exotic sources,consistent with other studies of the same field. The 20\% of UV-brightestgalaxies (M_{\rm UV}<-18.5) reionize 35\% of the survey volume,demonstrating that UV faint LyC emitters are crucial for reionization.