Chasing Cosmic Reionization: An Extremely Faint Highly Magnified Source at z=5.66 with high ξion
Abstract
We present JWST NIRSpec IFU spectroscopic measurements of one of the faintest (MUV>−13.6) known ionizing sources at z=5.66, dubbed Small And Lensed Source Arc, SALSA. This source is highly magnified (μ>100) by the lensing galaxy cluster Abell 2744, providing a unique opportunity to investigate the physical properties of faint sources in the Epoch of Reionization. We characterize SALSA's nebular emission using rest-frame UV and optical emission lines and investigate the relationship between its ionizing efficiency, nebular excitation, and chemical enrichment. We robustly detect Hα emission and use it to predict the Hβ flux assuming negligible dust attenuation. We also measure the [OIII]λ5007 emission and estimate oxygen abundance resulting in a high R3 index 2.82−0.25+0.34 and relatively low metallicity 12+log(O/H)= 7.43±0.09. SALSA presents a high ionizing production efficiency log(ξion)=25.49−0.08+0.09 Hz erg −1, consistent with theoretical models from very massive stars and constant star formation rate, and a high Lyα escape fraction fescLyα=0.39±0.14. These properties place SALSA among the most extreme star-forming sources known at this epoch.
Related
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- Investigating the star formation histories of galaxies from Cosmic Dawn to the Epoch of Reionization with the Santa Cruz SAM
BibTeX
@misc{rojasruiz2026chasing,
title = {{Chasing Cosmic Reionization: An Extremely Faint Highly Magnified Source at $z=5.66$ with high $ξ_\rm ion$}},
author = {Sofía Rojas-Ruiz and Matteo Messa and Eros Vanzella and Tommaso Treu and Pietro Bergamini and Giorgia Di Rosa and Marco Lombardi and Piero Rosati},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09281},
eprint = {2609.09281},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09281},
}
RIS
TY - UNPB
TI - Chasing Cosmic Reionization: An Extremely Faint Highly Magnified Source at z=5.66 with high ξ_ion
AU - Sofía Rojas-Ruiz
AU - Matteo Messa
AU - Eros Vanzella
AU - Tommaso Treu
AU - Pietro Bergamini
AU - Giorgia Di Rosa
AU - Marco Lombardi
AU - Piero Rosati
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.09281
UR - https://arxiv.org/abs/2609.09281
AB - We present JWST NIRSpec IFU spectroscopic measurements of one of the faintest (M_UV>−13.6) known ionizing sources at z=5.66, dubbed Small And Lensed Source Arc, SALSA. This source is highly magnified (μ>100) by the lensing galaxy cluster Abell 2744, providing a unique opportunity to investigate the physical properties of faint sources in the Epoch of Reionization. We characterize SALSA's nebular emission using rest-frame UV and optical emission lines and investigate the relationship between its ionizing efficiency, nebular excitation, and chemical enrichment. We robustly detect Hα emission and use it to predict the Hβ flux assuming negligible dust attenuation. We also measure the [OIII]λ5007 emission and estimate oxygen abundance resulting in a high R3 index 2.82_−0.25^+0.34 and relatively low metallicity 12+log(O/H)= 7.43±0.09. SALSA presents a high ionizing production efficiency log(ξ_ion)=25.49_−0.08^+0.09 Hz erg ^−1, consistent with theoretical models from very massive stars and constant star formation rate, and a high Lyα escape fraction f_esc^Lyα=0.39±0.14. These properties place SALSA among the most extreme star-forming sources known at this epoch.
ER -