Two Distinct Ancient Components in the Sculptor Dwarf Spheroidal Galaxy: First Results from the Dwarf Abundances and Radial Velocities Team

We have found evidence for the presence of two distinct ancient stellar components (both 10 Gyr old) in the Sculptor dwarf spheroidal galaxy. We used the ESO Wide Field Imager in conjunction with the Very Large Telescope/FLAMES spectrograph to study the properties of the resolved stellar population of Sculptor out to and beyond the tidal radius. We find that two components are discernible in the spatial distribution of horizontal branch stars in our imaging and in the [Fe/H] and Vhel distributions for our large sample of spectroscopic measurements. They can be generally described as a "metal-poor" component ([Fe/H] < -1.7) and a "metal- rich" component ([Fe/H] >0 -1.7). The metal-poor stars are more spatially extended than the metal-rich stars, and they also appear to be kinematically distinct. These results provide insight into the formation processes of small systems in the early universe and the conditions found there. Even this simplest of galaxies appears to have had a surprisingly complex early evolution.