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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Detection of star formation in a near-pristine pocket of the Universe

  • Louise Welsh1,2
  • Ryan Cooke1
  • Michele Fumagalli3,2
  • Rajeshwari Dutta4
  • Matteo Fossati3,5
  • Valentina D’Odorico2
5 affiliations
  1. 1Centre for Extragalactic Astronomy, Durham University , South Road, Durham DH1 3LE ,
  2. 2INAF - Osservatorio Astronomico di Trieste , via G. B. Tiepolo 11, I-34143 Trieste ,
  3. 3Università degli Studi di Milano-Bicocca Dipartimento di Fisica G. Occhialini, , Piazza della Scienza 3, 20126 Milano ,
  4. 4IUCAA , Postbag 4, Ganeshkhind, Pune 411007, Maharashtra ,
  5. 5INAF - Osservatorio Astronomico di Brera , Via Brera 28, 20122 Milano, via E. Bianchi 46, 23807 Merate ,
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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 km s−1 (LAE1) and Δv = −200 km s−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 1640Å emission flux of these sources, F(Hetextsc ii) <3.8× 10−19 erg s−1 cm−2 (3σ ) and F(Hetextsc 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.

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Cite

BibTeXRIS
BibTeX
@article{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},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag2035},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2035/8997903},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
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  - 2026/10/24
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag2035
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2035/8997903
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 km s−1 (LAE1) and Δv = −200 km s−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 1640Å emission flux of these sources, F(Hetextsc ii) <3.8× 10^−19 erg s^−1 cm^−2 (3σ ) and F(Hetextsc 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.
SN  - 0035-8711
SN  - 1365-2966
ER  -