EUROPEAN SPACE AGENCY

MIDIS: Unveiling the Role of Strong Hα Emitters During the Epoch of Reionization with JWST

DOI: 10.3847/1538-4357/ad4147 Bibcode: 2024ApJ...969...12R

Ilbert, O.; Östlin, G.; Güdel, M.; Colina, L.; Greve, T. R.; Walter, F.; Henning, Th.; van der Werf, P.; Ward, M.; Le Fèvre, O.; Kendrew, S.; Melinder, J.; Bik, A.; Annunziatella, M.; Caputi, K. I.; Hjorth, J.; Iani, E.; Rinaldi, P.; Eckart, A.; Labiano, A.; Vandenbussche, B.; Dayal, Pratika; Lagage, P. -O.; Waelkens, C.; Tikkanen, T.; Wright, G. S.; Crespo Gómez, A.; Álvarez-Márquez, J.; Boogaard, L.; Peissker, F.; García-Marín, M.; Costantin, L.; Gillman, S.; Jermann, I.; Langeroodi, D.; Moutard, T.; Ray, T.; Pye, J.; van Dishoeck, E.; Azzollini, R.; Bosman, S. E. I.; Meyer, R. A.; Perez Gonzalez, P. G.; Nørgard-Nielsen, H. U.

Netherlands, Denmark, Spain, Sweden, United Kingdom, Germany, United States, France, Italy, Ireland, Austria, Switzerland, Belgium

Abstract

By using an ultradeep JWST/MIRI image at 5.6 μm in the Hubble eXtreme Deep Field, we constrain the role of strong Hα emitters (HAEs) during "cosmic reionization" at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = ‑2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log10(ξion,0/(Hzerg‑1))=25.50‑0.12+0.10 . We show that ξ ion,0 positively correlates with Hα equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict fesc,LyC=4%‑2+3 , which results in log10(ξion/(Hzerg‑1))=25.55‑0.13+0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( Ṅion ) as Ṅion=1050.53±0.45s‑1Mpc‑3 . When comparing their Ṅion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization.

2024 • The Astrophysical Journal
JWST eHST 34
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