Probing patchy reionization with JWST : IGM opacity constraints from the Lyman α forest of galaxies in legacy extragalactic fields

Article Article scientifique Article Probing patchy reionization with JWST : IGM opacity constraints from the Lyman α forest of galaxies in legacy extragalactic fields eng 2025-08-11 2025-08-29 author Meyer Romain http://orcid.org/0000-0001-5492-4522 406183 Département d'astronomie (ASTRO) author Roberts-Borsani Guido http://orcid.org/0000-0002-4140-1367 412540 author Oesch Pascal http://orcid.org/0000-0001-5851-6649 846811 Département d'astronomie (ASTRO) author Ellis Richard S 17 10.1093/mnras/staf1312 0035-8711 https://academic.oup.com/mnras/article/542/3/1952/8230799 <p>We present the first characterization of the Gunn–Peterson trough in high-redshift galaxies using public James Webb Space Telescope (JWST) NIRSpec spectroscopy. This enables us to derive the first galaxy-based intergalactic medium (IGM) opacity measurements at the end of reionization. Using galaxy spectra has several advantages over quasar spectra: it enables measurements of the IGM opacity in any extragalactic field over a continuous redshift range $4\lesssim z\lesssim 7$, as well as measurements of the intrinsic Lyman $\beta$ opacity. Our novel constraints are in good agreement with state-of-the-art ground-based quasar Lyman $\alpha$ forest observations, and will become competitive as the number of JWST $z&gt;5$ galaxy spectra rapidly increases. We also provide the first constraints on the uncontaminated Lyman $\beta$ opacity at $5 \lt z \lt 6$. Finally, we demonstrate the power of JWST to connect the ionization state of the IGM to the sources of reionization in a single extragalactic field. We show that a previously reported galaxy overdensity and an excess of Lyman $\alpha$ emitters detected with JWST in GOODS-South at $z=5.8\!-\!5.9$ coincides with an anomalously low IGM opacity to Lyman $\alpha$ at this redshift. The local photoionization rate excess can be fully accounted for by the cumulative ionizing output of $M_{\rm {UV}}\lesssim -10$ galaxies in the overdensity, provided they have $\log _{10}\langle \xi _{\rm {ion}} f_{\rm {esc}} / \ [\rm {erg}^{-1}\rm {Hz}]\rangle \simeq 25$ (e.g. $\log _{10}\xi _{\rm {ion}} / \ [\rm {erg}^{-1}\rm {Hz}]=25.4$ and $f_{\rm {esc}}=40~{{\ \rm per\ cent}}$). Overall, this breakthrough offers a new way to connect the galaxy large-scale structure to the state of the IGM, potentially enabling us to precisely identify the sources of reionization.</p> Dewey 520 SERI MB22.00072 NASA NAS 5-03127 ESA CSA Danish National Research Foundation DNRF140 Swiss National Science Foundation A Revolutionary New Window on the First Galaxies 207349 CH Projects 26 Département d'astronomie 12 false 870 Direction de recherche "Galaxies et cosmologie observationnelle" Monthly notices of the Royal Astronomical Society 542 3 27feb101-0f2f-41e2-9985-cfd3262860ab Article (Published version) Public staf1312.pdf 3122593 application/pdf CC BY-4.0 c14060dcf9c39d871d57f46141048e80022c429387c7db7a54b47e439cce11e7 openAccess Faculté des sciences / Département d'astronomie

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Probing patchy reionization with JWST : IGM opacity constraints from the Lyman α forest of galaxies in legacy extragalactic fields	Monthly notices of the Royal Astronomical Society			2025	13	484

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Roberts-Borsani, Guido