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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).
Gatto et al. (Mon,) studied this question.