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Research

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Publication details for Dr Ryan Cooke

Hsyu, Tiffany, Cooke, Ryan J., Prochaska, J. Xavier & Bolte, Michael (2017). The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe. The Astrophysical Journal 845(2): L22.

Author(s) from Durham

Abstract

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found
in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor
galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast
spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic
data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely
metal-poor nature of this galaxy. Based on the weak [O III] λ4363 Å emission line, we estimate a direct oxygen
abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming
galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC
3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy
as it makes its first passage about a Milky Way–like galaxy.