Out of oxygen: extremely metal-poor galaxy candidates identified at 2.5 < z < 6.5 with deep JADES medium-band imaging
Abstract
The James Webb Space Telescope (JWST) is beginning to uncover a population of extremely metal-poor galaxies (EMPGs, Z lt 1 per cent Z⊙) at redshift z gt 3, mostly through serendipitous Near Infrared Spectrograph (NIRSpec) discoveries and blind slitless spectroscopy. To accelerate our understanding of pristine star formation, we further develop a methodology to identify EMPG candidates from photometry, utilizing the extensive deep Near Infrared Camera (NIRCam) medium-band imaging from the JWST Advanced Deep Extragalactic Survey (JADES). Our EMPG candidates at 2.5 lt z lt 6.5 exhibit strong photometric boosts by Hα, yet correspondingly weak boosts by [O iii] + Hβ, likely indicating extremely low metallicity to explain their lack of [O iii] emission. We further demand our EMPG candidates to have strong Balmer jumps, as revealed by medium-band imaging, to ensure that they are young starbursts, as opposed to broad-line active galactic nuclei/little red dots (AGN/LRDs), though contamination by dusty/dense-gas starbursts and highly obscured AGN remains a concern. Spectral Energy Distribution (SED)-fitting with near-pristine models (∼ 0.1–1 per cent Z⊙) indicates that our 14 EMPG candidates are low-mass (median M* ≈ 106.7 M⊙), faint dwarf galaxies (MUV ≈ −16.9), with high ionizing photon production efficiencies (log (ξ ion, obs/(Hz erg−1)) ≈ 26.0). Hence, these are plausible sites of near-pristine star formation, constituting ∼ 0.02–0.4 per cent of 2.5 lt z lt 6.5 galaxies at −19 lt MUV lt −16. We discuss this extremely metal-poor extension to the mass–metallicity relation. We forecast that deep (∼ 28 h) NIRCam slitless spectroscopy can identify bright EMPGs through strong Hβ but lack of [O iii] emission, or secure the redshifts of fainter systems through Hα detections. Highly multiplexed NIRSpec spectroscopy offers an alternate route to discovering the faintest pristine galaxies out to z=10, without requiring deep NIRCam medium-band and/or Mid-Infrared Instrument (MIRI) imaging to identify secure candidates.
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BibTeX
@article{trussler2026oxygen,
title = {{Out of oxygen: extremely metal-poor galaxy candidates identified at 2.5 < z < 6.5 with deep JADES medium-band imaging}},
author = {James Trussler and Daniel Eisenstein and Andrew Bunker and Alex Cameron and Stefano Carniani and Stéphane Charlot and Jacopo Chevallard and Christopher Conselice and Mirko Curti and Emma Curtis-Lake and Francesco D’eugenio and Eiichi Egami and Kevin Hainline and Ryan Hausen and Jakob Helton and Tiger Yu-Yang Hsiao and Zhiyuan Ji and Benjamin Johnson and Tobias Looser and Roberto Maiolino and Dávid Puskás and Pierluigi Rinaldi and Brant Robertson and Fengwu Sun and Sandro Tacchella and Hannah Übler and Christina Williams and Christopher Willmer and Joris Witstok and Zihao Wu},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = aug,
doi = {10.1093/mnras/stag1360},
eprint = {2603.15761},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05760738v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Out of oxygen: extremely metal-poor galaxy candidates identified at 2.5 < z < 6.5 with deep JADES medium-band imaging
AU - James Trussler
AU - Daniel Eisenstein
AU - Andrew Bunker
AU - Alex Cameron
AU - Stefano Carniani
AU - Stéphane Charlot
AU - Jacopo Chevallard
AU - Christopher Conselice
AU - Mirko Curti
AU - Emma Curtis-Lake
AU - Francesco D’eugenio
AU - Eiichi Egami
AU - Kevin Hainline
AU - Ryan Hausen
AU - Jakob Helton
AU - Tiger Yu-Yang Hsiao
AU - Zhiyuan Ji
AU - Benjamin Johnson
AU - Tobias Looser
AU - Roberto Maiolino
AU - Dávid Puskás
AU - Pierluigi Rinaldi
AU - Brant Robertson
AU - Fengwu Sun
AU - Sandro Tacchella
AU - Hannah Übler
AU - Christina Williams
AU - Christopher Willmer
AU - Joris Witstok
AU - Zihao Wu
PY - 2026
DA - 2026/08/25
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1360
UR - https://hal.science/hal-05760738v1
AB - The James Webb Space Telescope (JWST) is beginning to uncover a population of extremely metal-poor galaxies (EMPGs, Z lt 1 per cent Z_⊙) at redshift z gt 3, mostly through serendipitous Near Infrared Spectrograph (NIRSpec) discoveries and blind slitless spectroscopy. To accelerate our understanding of pristine star formation, we further develop a methodology to identify EMPG candidates from photometry, utilizing the extensive deep Near Infrared Camera (NIRCam) medium-band imaging from the JWST Advanced Deep Extragalactic Survey (JADES). Our EMPG candidates at 2.5 lt z lt 6.5 exhibit strong photometric boosts by Hα, yet correspondingly weak boosts by [O iii] + Hβ, likely indicating extremely low metallicity to explain their lack of [O iii] emission. We further demand our EMPG candidates to have strong Balmer jumps, as revealed by medium-band imaging, to ensure that they are young starbursts, as opposed to broad-line active galactic nuclei/little red dots (AGN/LRDs), though contamination by dusty/dense-gas starbursts and highly obscured AGN remains a concern. Spectral Energy Distribution (SED)-fitting with near-pristine models (∼ 0.1–1 per cent Z_⊙) indicates that our 14 EMPG candidates are low-mass (median M_* ≈ 10^6.7 M_⊙), faint dwarf galaxies (M_UV ≈ −16.9), with high ionizing photon production efficiencies (log (ξ _ion, obs/(Hz erg^−1)) ≈ 26.0). Hence, these are plausible sites of near-pristine star formation, constituting ∼ 0.02–0.4 per cent of 2.5 lt z lt 6.5 galaxies at −19 lt M_UV lt −16. We discuss this extremely metal-poor extension to the mass–metallicity relation. We forecast that deep (∼ 28 h) NIRCam slitless spectroscopy can identify bright EMPGs through strong Hβ but lack of [O iii] emission, or secure the redshifts of fainter systems through Hα detections. Highly multiplexed NIRSpec spectroscopy offers an alternate route to discovering the faintest pristine galaxies out to z=10, without requiring deep NIRCam medium-band and/or Mid-Infrared Instrument (MIRI) imaging to identify secure candidates.
SN - 0035-8711
SN - 1365-2966
ER -