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

Vedant Chandra, Charlie Conroy, Nelson Caldwell, Ana Bonaca, Rohan P. Naidu, Dennis Zaritsky, Phillip A. Cargile, Jiwon Jesse Han, Benjamin D. Johnson, Joshua S. Speagle, Yuan Sen Ting, Turner Woody

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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 age τ ≳ 12 Gyr and a mean metallicity 〈 [ Fe / H ] 〉 = − 1.84 − 0.18 + 0.16 , with a significant intrinsic metallicity dispersion σ [ Fe / H ] = 0.37 − 0.13 + 0.21 . We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosity M V ≈ −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.

Original languageEnglish (US)
Article number127
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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