The Metallicity Distribution of the Ultra-Faint Dwarf Galaxy Segue 1
- 1University of Chicago
Abstract
Ultra-faint dwarf galaxies (UFDs; stellar masses M * < 10 5 M ⊙ ) offer unique insights into early chemical evolution in low-mass systems. However, interpreting their metallicity distribution functions (MDFs) has been challenging due to limited spectroscopic samples, especially beyond the red giant branch. We present metallicities from the Ca II K absorption feature, measured from low-resolution ( R ∼ 1000 ) Keck/LRIS spectroscopy of 40 stars in the UFD Segue~1 ( M * ≈ 500 M ⊙ ), including both red giant branch and main-sequence turnoff stars, resulting in a metallicity sample more than six times larger than previously published data for Segue~1. The resulting MDF has an average [Fe/H] = − 2.52 ± 0.10 dex and a dispersion of σ = 0.59 ± 0.06 dex, and is best described by a single Gaussian, with no evidence for multimodal substructure. This is consistent with a continuous, short-duration ($$1~Gyr) episode of star formation and chemical enrichment prior to reionization. The nonzero metallicity spread reaffirms its classification as a galaxy. Segue~1 highlights the rich chemical enrichment histories present even in the least massive galaxies, and underscores the importance of deep spectroscopic follow-up to fully characterize these ancient stellar systems.
Versions
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BibTeX
@article{bissonette2026metallicity,
title = {{The Metallicity Distribution of the Ultra-Faint Dwarf Galaxy Segue 1}},
author = {Daisy Bissonette and Alexander P. Ji and Joshua D. Simon and Joss Bland-Hawthorn and Anirudh Chiti and Marla Geha and Ting S. Li and Anna Frebel and Alice M. Luna},
journal = {The Open Journal of Astrophysics},
year = {2026},
month = oct,
doi = {10.33232/001c.172763},
url = {https://astro.theoj.org/article/172763-the-metallicity-distribution-of-the-ultra-faint-dwarf-galaxy-segue-1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The Metallicity Distribution of the Ultra-Faint Dwarf Galaxy Segue 1
AU - Daisy Bissonette
AU - Alexander P. Ji
AU - Joshua D. Simon
AU - Joss Bland-Hawthorn
AU - Anirudh Chiti
AU - Marla Geha
AU - Ting S. Li
AU - Anna Frebel
AU - Alice M. Luna
PY - 2026
DA - 2026/10/20
JO - The Open Journal of Astrophysics
DO - 10.33232/001c.172763
UR - https://astro.theoj.org/article/172763-the-metallicity-distribution-of-the-ultra-faint-dwarf-galaxy-segue-1
AB - Ultra-faint dwarf galaxies (UFDs; stellar masses M * < 10 5 M ⊙ ) offer unique insights into early chemical evolution in low-mass systems. However, interpreting their metallicity distribution functions (MDFs) has been challenging due to limited spectroscopic samples, especially beyond the red giant branch. We present metallicities from the Ca II K absorption feature, measured from low-resolution ( R ∼ 1000 ) Keck/LRIS spectroscopy of 40 stars in the UFD Segue~1 ( M * ≈ 500 M ⊙ ), including both red giant branch and main-sequence turnoff stars, resulting in a metallicity sample more than six times larger than previously published data for Segue~1. The resulting MDF has an average [Fe/H] = − 2.52 ± 0.10 dex and a dispersion of σ = 0.59 ± 0.06 dex, and is best described by a single Gaussian, with no evidence for multimodal substructure. This is consistent with a continuous, short-duration ($$1~Gyr) episode of star formation and chemical enrichment prior to reionization. The nonzero metallicity spread reaffirms its classification as a galaxy. Segue~1 highlights the rich chemical enrichment histories present even in the least massive galaxies, and underscores the importance of deep spectroscopic follow-up to fully characterize these ancient stellar systems.
SN - 2565-6120
ER -