IRAC-Excess Galaxies in the NIRSpec Wide Survey: physical properties of bright EELGs at z∼7 and implications for Reionization
Abstract
We present an analysis of 23 Spitzer/IRAC excess galaxies at 5.66 < z < 7.64, observed as part of the NIRSpec Wide GTO survey. With NIRSpec PRISM spectroscopy, we measure a median rest-frame [OIII]+Hβ EW =1583~Å, consistent with predictions from the pre-JWST selection and we identify 17/23 (∼74%) of our sample as extreme emission line galaxies (EELGs), based on a selection of [OIII]+Hβ EW ≥1000~Å. The typical EELG is powered by star-formation rather than active galactic nuclei (AGN) based on their line widths, line ratios and absence of high-ionization lines, though we cannot exclude an AGN contribution in a few individual sources. We find that our luminous (⟨ MUV⟩=−20.7) EELG sample is characterised by sub-solar metallicities (7.38 < 12 + log(O/H) < 8.12), young stellar populations (t⋆ ∼ 20 Myr), and enhanced ionizing photon production efficiencies, with median log10(ξion/erg−1 Hz) = 25.62. We find that more UV luminous (∼ LUV, z=7∗) EELGs exhibit systematically lower O32 ratios than fainter (∼ 0.1× LUV∗) EELGs at fixed [OIII]+Hβ EW, indicating less extreme radiation fields and/or lower gas densities than their fainter counterparts. Furthermore, bright EELGs exhibit low neutral hydrogen column densities, consistent with a scenario in which they have largely ionized their circumgalactic medium (CGM). Despite this, we find very low Lyman-α escape fractions (<2\%), suggesting these systems reside in relatively small (≲ 0.25~pMpc) ionized regions of the intergalactic medium (IGM), possibly suggesting that bright galaxies have a minor contribution to reionization.
Related
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- A GLIMPSE OF THE 99%: A CENSUS OF THE FAINTEST GALAXIES DURING THE EPOCH OF REIONIZATION AND ITS IMPLICATIONS FOR GALAXY FORMATION MODELS
- Physical properties of star-forming clumps in nearby galaxies from CLAUDS and HSC-SSP
- The DAWN JWST Archive: A spectroscopically-informed population study of the physical properties of galaxies at z>2
BibTeX
@misc{ormerod2026iracexcess,
title = {{IRAC-Excess Galaxies in the NIRSpec Wide Survey: physical properties of bright EELGs at $z\sim7$ and implications for Reionization}},
author = {Katherine Ormerod and Renske Smit and Joris Witstok and Anna de Graaff and Michael V. Maseda and Andrew J. Bunker and Chris Willott},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.20332},
eprint = {2610.20332},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.20332},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - IRAC-Excess Galaxies in the NIRSpec Wide Survey: physical properties of bright EELGs at z∼7 and implications for Reionization
AU - Katherine Ormerod
AU - Renske Smit
AU - Joris Witstok
AU - Anna de Graaff
AU - Michael V. Maseda
AU - Andrew J. Bunker
AU - Chris Willott
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.20332
UR - https://arxiv.org/abs/2610.20332
AB - We present an analysis of 23 Spitzer/IRAC excess galaxies at 5.66 < z < 7.64, observed as part of the NIRSpec Wide GTO survey. With NIRSpec PRISM spectroscopy, we measure a median rest-frame [OIII]+Hβ EW =1583~Å, consistent with predictions from the pre-JWST selection and we identify 17/23 (∼74%) of our sample as extreme emission line galaxies (EELGs), based on a selection of [OIII]+Hβ EW ≥1000~Å. The typical EELG is powered by star-formation rather than active galactic nuclei (AGN) based on their line widths, line ratios and absence of high-ionization lines, though we cannot exclude an AGN contribution in a few individual sources. We find that our luminous (⟨ M_UV⟩=−20.7) EELG sample is characterised by sub-solar metallicities (7.38 < 12 + log(O/H) < 8.12), young stellar populations (t_⋆ ∼ 20 Myr), and enhanced ionizing photon production efficiencies, with median log_10(ξ_ion/erg^−1 Hz) = 25.62. We find that more UV luminous (∼ L_UV, z=7^∗) EELGs exhibit systematically lower O32 ratios than fainter (∼ 0.1× L_UV^∗) EELGs at fixed [OIII]+Hβ EW, indicating less extreme radiation fields and/or lower gas densities than their fainter counterparts. Furthermore, bright EELGs exhibit low neutral hydrogen column densities, consistent with a scenario in which they have largely ionized their circumgalactic medium (CGM). Despite this, we find very low Lyman-α escape fractions (<2\%), suggesting these systems reside in relatively small (≲ 0.25~pMpc) ionized regions of the intergalactic medium (IGM), possibly suggesting that bright galaxies have a minor contribution to reionization.
ER -