2018MNRAS.480..251C

We report the discovery of clear observational signs of past accretion/merger events in one of the Milky Way satellite galaxies, the Sextans dwarf spheroidal (dSph). These were uncovered in the spatial distribution, internal kinematics, and metallicity properties of Sextans stars using literature CTIO/DECam photometric and Magellan/MMFS spectroscopic catalogues. We find the spatial distribution of stars to vary as a function of the colour/metallicity, being rather regular and round for the blue (metal-poor) red giant branch and main-sequence turn-off stars but much more elliptical and irregularly shaped for the red (metal-rich) ones, with a distinct 'shell-like' overdensity in the northeast side. We also detect kinematic anomalies, in the form of a 'ring-like' feature with a considerably larger systemic line-of-sight velocity and lower metallicity than the rest of stars; even the photometrically selected component with a regular looking spatial distribution displays complex kinematics. With a stellar mass of just ∼5×10⁵ M_☉, Sextans becomes the smallest galaxy presenting clear observational signs of accretion to date.