September 23, 2025Open Access

Central Concentration and Escape of Ionizing Photons in Galaxies at the Epoch of Reionization

CLCheqiu LyuUniversity of Science and Technology of China EWEnci WangUniversity of Science and Technology of China JWJunxian WangUniversity of Science and Technology of China

Key Points

Galaxies exhibit high ionizing photon production efficiencies, especially in central regions, driving cosmic reionization.
The study analyzes 189 compact galaxies at redshifts 6.7-7.6, focusing on star formation and ionizing photon escape.
Findings indicate outside-in growth and enhanced star formation histories at z=7, highlighting the inner regions' significance.
Extreme [OIII]+Hβ equivalent widths and steep UV slopes point toward efficient photon production and escape in lower-mass systems.

Abstract

Compact, low-mass galaxies with strong nebular emission are considered promising candidates for efficient ionizing photon production and escape. We present a spatially resolved analysis of 189 galaxies at redshifts z 6. 7-7. 6 in JADES GOODS-N and GOODS-S fields and selected via JWST/NIRCam F410M filter. By employing annular photometry and spectral energy distribution fitting across rest-frame UV to optical wavelengths, we investigate the internal structure of star formation, ionizing photon production and escape, as well as the resolved star formation histories within these galaxies. We find that these galaxies exhibit compact, centrally concentrated, and bursty star formation, especially in lower-mass systems ( (M_*/ M_{}) 1000 Å), high ionizing photon production efficiencies (ξ₈₎₍ 10^25. 6 Hz erg^-1), steep UV slopes (-2. 3), and elevated escape fractions (f₄ₒ₂ > 0. 08), with all these properties peaking in the inner regions. These findings reveal outside-in growth and rising star formation histories at z 7, with the central regions of them playing a pivotal role in driving cosmic reionization.

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