The Metallicity Distribution of the Ultra-Faint Dwarf Galaxy Segue 1
Abstract
Ultra-faint dwarf galaxies (UFDs; stellar masses M* < 105 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 CaII 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
Related
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BibTeX
@misc{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},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.12810},
eprint = {2605.12810},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.12810},
note = {CC BY 4.0},
}
RIS
TY - UNPB
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 - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2605.12810
UR - https://arxiv.org/abs/2605.12810
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 CaII 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.
ER -