Detection of star formation in a near-pristine pocket of the Universe
Abstract
We detect two high-confidence star-forming sources in the environment of a chemically near-pristine ([Fe/H] <−3.66 ;2σ) Damped Lyα system (DLA) using Keck/KCWI. These are found via the hydrogen Lyα emission line at Δv=−1200 kms−1 (LAE1) and Δv = −200 kms−1 (LAE2) relative to the DLA redshift (zabs = 3.078) at an impact parameter of b=66 physical kpc and b=137 physical kpc. We measure Lyα fluxes of F(Lyα)LAE1 =4.4± 0.7×10−18 erg s−1 cm−2 and F(Lyα)LAE2 =3.8± 0.9×10−18 erg s−1 cm−2. This marks the first detection of star formation in the environment of a chemically near-pristine DLA. We use red channel Keck/KCRM data to place limits on the associated He II 1640 A emission flux of these sources, F(He II)<3.8×10−19 erg s−1 cm−2 (3σ) and F(He II) <3.7×10−19 erg s−1 cm−2 (3σ). The weak and narrow properties of the Lyα emission, combined with the inferred position on the mass-metallicity relation, suggest a metal-paucity of these galaxies. Future rest-frame optical observations are required to pin down the metallicity of LAE1 and LAE2 and test if chemically near-pristine DLAs can be used as a signpost to search for primitive, metal-poor galaxies 2 Gyrs after the Big Bang.
Versions
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BibTeX
@misc{welsh2026detection,
title = {{Detection of star formation in a near-pristine pocket of the Universe}},
author = {Louise Welsh and Ryan Cooke and Michele Fumagalli and Rajeshwari Dutta and Matteo Fossati and Valentina D'Odorico},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.36042},
eprint = {2610.36042},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.36042},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Detection of star formation in a near-pristine pocket of the Universe
AU - Louise Welsh
AU - Ryan Cooke
AU - Michele Fumagalli
AU - Rajeshwari Dutta
AU - Matteo Fossati
AU - Valentina D'Odorico
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.36042
UR - https://arxiv.org/abs/2610.36042
AB - We detect two high-confidence star-forming sources in the environment of a chemically near-pristine ([Fe/H] <−3.66 ;2σ) Damped Lyα system (DLA) using Keck/KCWI. These are found via the hydrogen Lyα emission line at Δv=−1200 kms^−1 (LAE1) and Δv = −200 kms^−1 (LAE2) relative to the DLA redshift (z_abs = 3.078) at an impact parameter of b=66 physical kpc and b=137 physical kpc. We measure Lyα fluxes of F(Lyα)_LAE1 =4.4± 0.7×10^−18 erg s^−1 cm^−2 and F(Lyα)_LAE2 =3.8± 0.9×10^−18 erg s^−1 cm^−2. This marks the first detection of star formation in the environment of a chemically near-pristine DLA. We use red channel Keck/KCRM data to place limits on the associated He II 1640 A emission flux of these sources, F(He II)<3.8×10^−19 erg s^−1 cm^−2 (3σ) and F(He II) <3.7×10^−19 erg s^−1 cm^−2 (3σ). The weak and narrow properties of the Lyα emission, combined with the inferred position on the mass-metallicity relation, suggest a metal-paucity of these galaxies. Future rest-frame optical observations are required to pin down the metallicity of LAE1 and LAE2 and test if chemically near-pristine DLAs can be used as a signpost to search for primitive, metal-poor galaxies 2 Gyrs after the Big Bang.
ER -