# Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≍ 1.4 Mpc

DOI:
10.3847/2041-8213/ac85ee
Publication date:
08/08/2022
Main author:
Sand, David J.
IAA authors:
Karunakaran, Ananthan
Authors:
Sand, David J.;Mutlu-Pakdil, Burçin;Jones, Michael G.;Karunakaran, Ananthan;Wang, Feige;Yang, Jinyi;Chiti, Anirudh;Bennet, Paul;Crnojević, Denija;Spekkens, Kristine
Journal:
The Astrophysical Journal
Refereed:
Yes
Publication type:
Article
Volume:
935
Pages:
L17
Abstract:
We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D = 1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ~500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80 ± 40 pc and an absolute magnitude of {M}_{V}=-{6.9}_{-0.6}^{+0.5}$mag ( {L}_{V}=({5}_{-2}^{+4})\times {10}^{4}$ L <SUB>⊙</SUB>), which is again comparable to the Milky Way's ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color-magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating \mathrm{log}({\mathrm{SFR}}_{\mathrm{NUV}}/{M}_{\odot }\,{\mathrm{yr}}^{-1})\lt -5.4\$ for star formation on ≲100 Myr timescales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group. *This paper includes data gathered with the 6.5 m Magellan Telescope at Las Campanas Observatory, Chile.
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