A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy by Vedant Chandra et al. on Wednesday 30 November

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

$25^\circ \times 1^\circ$ 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 $\tau \gtrsim 12$ Gyr and a mean

metallicity $\langle\text{[Fe/H]}\rangle = -1.84_{-0.18}^{+0.16}$, with a

significant intrinsic metallicity dispersion $\sigma_{ \text{[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_{\text{V}} \approx

-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.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2207.13717v2