Breaking through the cosmic fog: JWST/NIRSpec constraints on ionizing photon escape in reionization-era galaxies

Article Article scientifique Article Breaking through the cosmic fog: JWST/NIRSpec constraints on ionizing photon escape in reionization-era galaxies eng 2026-03-17 2026-03 author Giovinazzo Emma 0009-0004-3835-0089 403264 Département d'astronomie (ASTRO) author Oesch Pascal 0000-0001-5851-6649 846811 Département d'astronomie (ASTRO) author Weibel Andrea Daniel 0000-0001-8928-4465 970671 Département d'astronomie (ASTRO) author Meyer Romain 0000-0001-5492-4522 406183 Département d'astronomie (ASTRO) author Witten Callum 0000-0002-1369-6452 author Bhagwat Aniket author Brammer Gabriel author Chisholm John author de Graaff Anna author Gottumukkala Rashmi author Jecmen Michelle 0009-0004-4725-8559 author Katz Harley author Leja Joel 0000-0001-6755-1315 author Marques-Chaves Rui 0000-0001-8442-1846 author Maseda Michael 0000-0003-0695-4414 author Shivaei Irene author Trebitsch Maxime 0000-0002-6849-5375 author Verhamme Anne 0000-0002-2201-1865 135594 Département d'astronomie (ASTRO) A352 10.1051/0004-6361/202556204 0004-6361 https://www.aanda.org/10.1051/0004-6361/202556204 Aims. The escape fraction of Lyman continuum photons ( f esc (LyC)) is the last key unknown in our understanding of cosmic reionization. Directly estimating the escape fraction ( f esc ) of ionizing photons in the epoch of reionization (EoR) is impossible, due to the opacity of the intergalactic medium (IGM). However, a high f esc leaves clear imprints in the spectrum of a galaxy, due to reduced nebular line and continuum emission, which also leads to bluer UV continuum slopes ( β UV ). Methods. In this work, we exploited the large archive of deep James Webb Space Telescope (JWST) NIRSpec spectra from the DAWN JWST archive to analyze over 1400 galaxies at 5 < z spec < 10 and constrain their f esc based on spectral-energy-distribution fitting enhanced with a picket-fence model. We identify 71 high-confidence sources with significant f esc based on Bayes-factor analysis strongly favoring f esc > 0 over f esc = 0 solutions. We compare the characteristics of this high-escape subset against both the parent sample and established diagnostics including β UV slope, O32, and SFR surface density (Σ SFR ). Results. For the overall sample, we find that most sources have a low escape fraction (< 1%); however, a small subset of sources seems to emit a large number of their ionizing photons into the IGM, such that the average f esc is found to be ∼10%, as needed for galaxies to drive reionization. Conclusions. Although uncertainties remain regarding recent burstiness and the intrinsic stellar ionizing-photon output at low metallicities, our results demonstrate the unique capability of JWST/NIRSpec to identify individual LyC leakers, measure average f esc , and thus constrain the drivers of cosmic reionization. Dewey 520 Swiss State Secretariat for Education, Research and Innovation MB22.00072 Danish National Research Foundation 140 Swiss National Science Foundation A Revolutionary New Window on the First Galaxies 207349 CH 26 Département d'astronomie 12 false Astronomy & astrophysics 707 9b386db5-5b85-455f-8bcc-684d79d8a277 Article (Published version) Public Article_scientifique_from_crossref.pdf 1780869 application/pdf CC BY-4.0 04247e4656ae1cbaea2d9b139ea7df95649912f128981a751e5c189f7e835a38 openAccess Faculté des sciences / Département d'astronomie

Title	Published in	Year	Views	Downloads

Breaking through the cosmic fog: JWST/NIRSpec constraints on ionizing photon escape in reionization-era galaxies	Astronomy & astrophysics	2026	2	308
Transfert radiatif Lyman-alpha dans les galaxies		2008	716	911

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