A Ghost in Boötes: The Least-Luminous Disrupted Dwarf Galaxy
Abstract
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 $\langle [\mathrm{Fe}/{\rm{H}}]\rangle =-{1.84}_{-0.18}^{+0.16}$ , with a significant intrinsic metallicity dispersion ${\sigma }_{[\mathrm{Fe}/{\rm{H}}]}={0.37}_{-0.13}^{+0.21}$ . 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2022
- DOI:
- 10.3847/1538-4357/ac9b4b
- arXiv:
- arXiv:2207.13717
- Bibcode:
- 2022ApJ...940..127C
- Keywords:
-
- Dwarf galaxies;
- Low surface brightness galaxies;
- Stellar streams;
- 416;
- 940;
- 2166;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages, 10 figures. Accepted to ApJ