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Title: A Ghost in Boötes: The Least-Luminous Disrupted Dwarf Galaxy

We report the discovery of Specter, a disrupted ultrafaint dwarf galaxy revealed by the H3 Spectroscopic Survey. We detected this structure via a pair of comoving metal-poor stars at a distance of 12.5 kpc, and further characterized it with Gaia astrometry and follow-up spectroscopy. Specter is a 25° × 1° stream of stars that is entirely invisible until strict kinematic cuts are applied to remove the Galactic foreground. The spectroscopic members suggest a stellar ageτ≳ 12 Gyr and a mean metallicity[Fe/H]=1.840.18+0.16, with a significant intrinsic metallicity dispersionσ[Fe/H]=0.370.13+0.21. We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosityMV≈ −2.6, Specter is by far the least-luminous dwarf galaxy stream known. We estimate that dozens of similar streams are lurking below the detection threshold of current search techniques, and conclude that spectroscopic surveys offer a novel means to identify extremely low surface brightness structures.

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DOI PREFIX: 10.3847
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Journal Name:
The Astrophysical Journal
Medium: X Size: Article No. 127
["Article No. 127"]
Sponsoring Org:
National Science Foundation
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