PRISMS: U37126, a very blue ISM-naked starburst at z = 10.255 with a nearly 100% Lyman continuum escape fraction
24 affiliations
- 1Geneva Observatory, Department of Astronomy, University of Geneva
- 2Centro de Astrobiología (CAB), CSIC-INTA
- 3European Space Agency (ESA), ESA Office, Space Telescope Science Institute
- 4Department of Astronomy, Indiana University
- 5Departamento de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid
- 6Leiden Observatory, Leiden University
- 7INAF – Osservatorio Astronomico di Roma
- 8Kapteyn Astronomical Institute, University of Groningen
- 9Space Telescope Science Institute (STScI)
- 10Center for Frontier Science, Chiba University
- 11David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto
- 12Dunlap Institute for Astronomy and Astrophysics
- 13Institute for Cosmic Ray Research, The University of Tokyo
- 14Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba
- 15Tomonaga Center for the History of the Universe (TCHoU), Faculty of Pure and Applied Sciences, University of Tsukuba
- 16Department of Astronomy, University of Texas
- 17Institute of Science and Technology Austria (ISTA)
- 18Department of Physics, School of Advanced Science and Engineering, Faculty of Science and Engineering, Waseda University
- 19Waseda Research Institute for Science and Engineering, Faculty of Science and Engineering, Waseda University
- 20DARK, Niels Bohr Institute, University of Copenhagen
- 21University of Massachusetts Amherst
- 22Department of Astronomy, Stockholm University, Oscar Klein Centre, AlbaNova University Centre
- 23AURA for the European Space Agency (ESA), Space Telescope Science Institute
- 24UK Astronomy Technology Centre, Royal Observatory Edinburgh
Abstract
We present very deep (≈11 hours on-source) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright ( M UV ≃ −20) mildly lensed ( μ ≃ 2.2) galaxy at z = 10.255. The continuum emission is well detected in the NIRSpec and MIRI spectra, but no nebular recombination or metal emission lines are observed ( EW 0 (H β +[O III ]) ≤ 300 Å and EW 0 (H α ) ≤ 400 Å at 3 σ ). Combined with the exceptionally blue UV continuum slope, β UV ≃ −2.9, and flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires a very high ionizing photon production efficiency, log( ξ ion /Hz erg −1 ) ≃ 25.75, and a nearly unity Lyman continuum escape fraction, of f esc ≥ 86% (3 σ ) based on the H α flux limit and f esc = 0.94 ± 0.06 derived independently from fitting the spectral energy distribution (SED). The best-fit SED yields a (delensed) stellar mass of M ★ ≃ 10 7.8 M ⊙ and a star formation rate SFR ≃ 10 M ⊙ yr −1 (specific SFR ∼ 160 Gyr −1 ). Together with its very compact size, r eff ≃ 61 pc, this yields a very high stellar mass and SFR surface densities, Σ M ★ ≃ 3 × 10 3 M ⊙ pc −2 and Σ SFR ≃ 400 M ⊙ yr −1 kpc −2 . Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing a so-called interstellar medium-naked starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, which allowed most Lyman continuum photons to escape. Finally, we show that even a small fraction of galaxies such as U37126 (≃3–6%), with an extreme Lyman continuum production and escape, might contribute disproportionately (≃50–100%) to the ionizing photon budget during cosmic reionization.
Related
- PRISMS GHZ8: Evidence for a Young Burst and Potential Merger Activity at z=10.23
- PRISMS/U13151. A Glimpse into the Earliest Phases of Galaxy Formation through an Ultra-Faint System ≈ 500 Myr after the Big Bang
- PRISMS. GHZ1. A standard tale of galaxy evolution with atypical ionizing conditions at z=9.878
- Can the ∼ 5 kpc starburst ring in MW create eROSITA bubbles?
- The Evolution of the Circumgalactic Medium after a starburst in DESI Post-Starburst Galaxies
BibTeX
@article{marqueschaves2026prisms,
title = {{PRISMS: U37126, a very blue ISM-naked starburst at z = 10.255 with a nearly 100% Lyman continuum escape fraction}},
author = {R. Marques-Chaves and Javier Álvarez-Márquez and Luis Colina and Sarah Kendrew and Abdurro'uf and Carmen Blanco-Prieto and Leindert Boogaard and M. Castellano and K. I. Caputi and Alejandro Crespo Gómez and A. Fontana and Yoshinobu Fudamoto and S. Fujimoto and M. García-Marín and Yuichi Harikane and Santosh Harish and Takuya Hashimoto and T. Hsiao and Edoardo Iani and Akio K. Inoue and Danial Langeroodi and R. Lin and Jens Melinder and Lorenzo Napolitano and Göran Östlin and Pablo G. Pérez‐González and Carlota Prieto-Jiménez and P. Rinaldi and Bruno Rodríguez Del Pino and Paola Santini and Yuma Sugahara and A. Varo-O'ferral and G. S. Wright and J. Zavala},
journal = {Astronomy and Astrophysics},
year = {2026},
month = jun,
doi = {10.1051/0004-6361/202659281},
url = {https://doi.org/10.1051/0004-6361/202659281},
note = {CC BY},
}
RIS
TY - JOUR
TI - PRISMS: U37126, a very blue ISM-naked starburst at z = 10.255 with a nearly 100% Lyman continuum escape fraction
AU - R. Marques-Chaves
AU - Javier Álvarez-Márquez
AU - Luis Colina
AU - Sarah Kendrew
AU - Abdurro'uf
AU - Carmen Blanco-Prieto
AU - Leindert Boogaard
AU - M. Castellano
AU - K. I. Caputi
AU - Alejandro Crespo Gómez
AU - A. Fontana
AU - Yoshinobu Fudamoto
AU - S. Fujimoto
AU - M. García-Marín
AU - Yuichi Harikane
AU - Santosh Harish
AU - Takuya Hashimoto
AU - T. Hsiao
AU - Edoardo Iani
AU - Akio K. Inoue
AU - Danial Langeroodi
AU - R. Lin
AU - Jens Melinder
AU - Lorenzo Napolitano
AU - Göran Östlin
AU - Pablo G. Pérez‐González
AU - Carlota Prieto-Jiménez
AU - P. Rinaldi
AU - Bruno Rodríguez Del Pino
AU - Paola Santini
AU - Yuma Sugahara
AU - A. Varo-O'ferral
AU - G. S. Wright
AU - J. Zavala
PY - 2026
DA - 2026/06/23
JO - Astronomy and Astrophysics
DO - 10.1051/0004-6361/202659281
UR - https://doi.org/10.1051/0004-6361/202659281
AB - We present very deep (≈11 hours on-source) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright ( M UV ≃ −20) mildly lensed ( μ ≃ 2.2) galaxy at z = 10.255. The continuum emission is well detected in the NIRSpec and MIRI spectra, but no nebular recombination or metal emission lines are observed ( EW 0 (H β +[O III ]) ≤ 300 Å and EW 0 (H α ) ≤ 400 Å at 3 σ ). Combined with the exceptionally blue UV continuum slope, β UV ≃ −2.9, and flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires a very high ionizing photon production efficiency, log( ξ ion /Hz erg −1 ) ≃ 25.75, and a nearly unity Lyman continuum escape fraction, of f esc ≥ 86% (3 σ ) based on the H α flux limit and f esc = 0.94 ± 0.06 derived independently from fitting the spectral energy distribution (SED). The best-fit SED yields a (delensed) stellar mass of M ★ ≃ 10 7.8 M ⊙ and a star formation rate SFR ≃ 10 M ⊙ yr −1 (specific SFR ∼ 160 Gyr −1 ). Together with its very compact size, r eff ≃ 61 pc, this yields a very high stellar mass and SFR surface densities, Σ M ★ ≃ 3 × 10 3 M ⊙ pc −2 and Σ SFR ≃ 400 M ⊙ yr −1 kpc −2 . Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing a so-called interstellar medium-naked starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, which allowed most Lyman continuum photons to escape. Finally, we show that even a small fraction of galaxies such as U37126 (≃3–6%), with an extreme Lyman continuum production and escape, might contribute disproportionately (≃50–100%) to the ionizing photon budget during cosmic reionization.
SN - 0004-6361
SN - 1432-0746
ER -