Galaxies in the Epoch of Reionization Are All Bark and No Bite -- Plenty of Ionizing Photons, Low Escape Fractions
Casey Papovich (1), Justin W. Cole (1), Weida Hu (1), Steven L. Finkelstein (2), Lu Shen (1), Pablo Arrabal Haro (3), Ricardo O. Amor\'in (4), Bren Backhaus (5), Micaela B. Bagley (2,5), Rachana Bhatawdekar (6), Antonello Calabr\'o (7), Adam C. Carnall (8), Nikko Cleri (9)

TL;DR
This study uses JWST data to analyze the ionizing photon production and escape fractions of early galaxies, finding high photon production but low escape fractions, which impacts models of cosmic reionization.
Contribution
It provides the first comprehensive analysis of ionizing photon escape fractions in high-redshift galaxies using JWST data, revealing low escape fractions despite high photon production.
Findings
Escape fractions are low, averaging 2.6-6.5%, with weak redshift evolution.
Ionizing photon production efficiency increases with redshift and decreases with UV luminosity.
Galaxies brighter than M(UV) < -16 can reionize the universe by z~6, but escape fractions are insufficient for early reionization.
Abstract
Early results from JWST suggest that epoch-of-reionization (EoR) galaxies produce copious ionizing photons, which, if they escape efficiently, could cause reionization to occur too early. We study this problem using \jwst\ imaging and prism spectroscopy for 412 galaxies at 4.5 < z < 9.0. We fit these data simultaneously with stellar-population and nebular-emission models that include a parameter for the fraction of ionizing photons that escape the galaxy, . We find that the ionization production efficiency, = Q(H) / L(UV), increases with redshift and decreasing UV luminosity, but shows significant scatter, = 0.3 dex. The inferred escape fractions averaged over the population are low, ranging from = \% at 6 < z < 9 to \% at 4.5 < z < 6 with weak or no indication of…
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Taxonomy
TopicsGalaxies: Formation, Evolution, Phenomena · Astronomy and Astrophysical Research · Space Technology and Applications
