REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization

Komarova, L, Stefanon, M, Laza-Ramos, A, Algera, HSB, Aravena, M, Bouwens, R, Bowler, R, da Cunha, E, Dayal, P, Ferrara, A, Fisher, R, Nanayakkara, T, Rowland, LE, Schouws, S, Smit, R ORCID: 0000-0001-8034-7802, Sommovigo, L, Stark, DP and van der Werf, P (2026) REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization. The Astrophysical Journal, 1000 (2). ISSN 0004-637X

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Abstract

Measuring the ionizing photon production efficiency ξion,0—the ratio of the ionizing photon output rate QH0 to the UV continuum luminosity LUV—in galaxies at z > 6 is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of ξion,0 for 12 exceptionally bright (MUV ∼ −22 mag) star-forming galaxies at z ∼ 7 from the Reionization Era Bright Emission Line Survey (REBELS). These measurements are based on JWST NIRSpec/Integral Field Unit PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes Hα, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global log(sion,0) values ranging from 25.19 ± 0.11 to 25.61 ± 0.11, with a weighted mean of 25.44 ± 0.15, consistent with the canonical value of ∼25.3. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in the ionizing photon production efficiency, finding a broader range, from 24.52 ± 0.21 to 26.18 ± 0.61. We identify strong correlations between ξion,0 and the specific star formation rate, star formation surface density, Hβ equivalent width, and stellar mass. Clumps with the highest ξion,0 exhibit EW0(Hβ) ≥ 150 Å, consistent with young stellar ages. From previous Lyα measurements in three galaxies, we estimate a typical Lyα escape fraction of fesc,Lyα ∼ 2%, suggesting similar or lower escape fractions for LyC photons. Combining this with our Hα measurements, we infer ionized bubble sizes ∼1 pMpc, aligned with expectations from Lyα-detected systems and reionization models

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	IOP Publishing
Date of acceptance:	14 February 2026
Date of first compliant Open Access:	12 June 2026
Date Deposited:	12 Jun 2026 10:11
Last Modified:	12 Jun 2026 10:11
DOI or ID number:	10.3847/1538-4357/ae474f
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28818

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