2024A&A...681L..13G

We report the discovery of a significant and compact over-density of old and metal-poor stars in the fourth data release of the KiDS survey (DR4). The discovery is confirmed by deeper HSC-SSP data revealing the old main sequence turn-off of a stellar system located at a distance from the sun of D_⊙ = 145_–13⁺¹⁴ kpc in the direction of the Sextans constellation. The system has an absolute integrated magnitude (M_V = -3.9 ± 0.4), half-light radius (r_h = 193_–46⁺⁶¹ pc), and ellipticity (e = 0.46_–0.15^+0.11) values that are typical of ultra-faint dwarf galaxies (UFDs). The central surface brightness is near the lower limits of known local dwarf galaxies of a similar integrated luminosity, as expected for stellar systems that have escaped detection until now. The distance of the newly found system suggests that it is likely to be a satellite of our own Milky Way and we have thus tentatively named it Sextans II (KiDS-UFD-1).