Paper

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D\\(\\approx\\)1.4 Mpc

Mutlu-Pakdil, B, Chiti, A, Bennet, P, Sand, D J, Karunakaran, A, Crnojević, D, Spekkens, K, Yang, J, Wang, F, Jones, M G

2022

Overview

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 \\(\\sim\\)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\\(\\pm\\)40 pc, and an absolute magnitude of \\(M_V\\)=\\(-\\)6.9\\(^{+0.5}_{-0.6}\\) mag (\\(L_V\\)=\\((5^{+4}_{-2})\\times\\)10\\(^4\\) \\(L_{\\odot}\\)), 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 \\(\\log (\\mathrm{SFR_{NUV}/M_\\odot \\, yr^{-1}}) < -5.4\\) for star formation on \\(\\lesssim\\)100 Myr time scales. 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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Color-magnitude diagram / Dwarf galaxies / Galactic evolution / Ionization / Local group (astronomy) / Neutral gases / Physical properties / Quenching / Red giant stars / Satellites / Star & galaxy formation