We report a possible discovery of a relic star cluster in the Sextans dwarf spheroidal galaxy .
Using the hk index ( \equiv ( Ca - b ) - ( b - y ) ) as a photometric metallicity indicator , we discriminate the metal-poor and metal-rich stars in the galaxy and find unexpected number density excess of metal-poor stars located 7 \arcmin .7 ( \sim 190 pc in projected distance ) away from the known galactic center .
The V - I color - magnitude diagram ( CMD ) for stars around the density excess reveals that both the main sequence and the giant branch are considerably narrower and redder than the bulk of field stars in Sextans .
Our stellar population models show ( a ) that the narrow CMD is best reproduced by a simple stellar population with an age of \sim 13 Gyr and [ Fe/H ] of \sim - 2.3 dex , and ( b ) that the redder V - I color of the hk -weak population is explained only if it is \sim 2 Gyr older than the field stars .
The results lead us to conclude that the off-centered density peak is likely associated with an old , metal-poor globular cluster .
The larger spatial extent ( > 80 pc in radius ) and the smaller number of stars ( \sim 1000 ) than typical globular clusters point to a star cluster that is in the process of dissolution .
The finding serves as the first detection of a surviving star cluster in Sextans , supporting previous suggestions of the presence of star cluster remnants in the galaxy .
If confirmed , the survival of a relic star cluster until now implies a cored dark matter halo profile for this dwarf galaxy .