Speakers: Andrea Bolamperti (Università degli Studi di Padova)
Aims. The demographics of the production and escape of ionizing photons from UV-faint early galaxies is a key unknown in discovering the primary drivers of reionization. With the advent of JWST it is finally possible to observe the rest-frame optical nebular emission from individual sub-L* z > 3 galaxies to measure the production rate of ionizing photons, ξion.
Methods. Here we study a sample of 370 z ∼ 3 − 7 galaxies spanning −23 < MUV < −15.5 (median MUV ≈ −18) with deep multiband HST and JWST/NIRCam photometry covering the rest-UV to optical from the GLASS and UNCOVER JWST surveys. Our sample includes 102 galaxies with Lyman-alpha emission detected in MUSE spectroscopy. We use Hα fluxes inferred from NIRCam photometry to estimate the production rate of ionizing photons which do not escape these galaxies ξion(1 − fesc).
Results. We find median log10 ξion (1 − fesc) = 25.33 ± 0.47, with a broad intrinsic scatter 0.42 dex, implying a broad range of galaxy properties and ages in our UV-faint sample. Galaxies detected with Lyman-alpha have ∼ 0.1 dex higher ξion(1 − fesc), which is explained by their higher Hα EW distribution, implying younger ages, higher sSFR and thus more O/B stars. We find significant trends of increasing ξion(1 − fesc) with increasing Hα EW, decreasing UV luminosity, and decreasing UV slope, implying the production of ionizing photons is enhanced in young galaxies with assumed low metallicities. We find no significant evidence for sources with very high ionizing escape fraction (fesc > 0.5) in our sample, based on their photometric properties, even amongst the Lyman-alpha selected galaxies.
Conclusions. This work demonstrates that considering the full distribution of ξion across galaxy properties is important for assessing the primary drivers of reionization.