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We present wide-field photometry of resolved stars in the nearby Sculptordwarf spheroidal galaxy using CTIO/MOSAIC, going down to the oldest MainSequence Turn-Off. The accurately flux calibrated wide field Colour-MagnitudeDiagrams can be used to constrain the ages of different stellar populations,and also their spatial distribution. The Sculptor dSph contains a predominantlyancient stellar population (>10 Gyr old) which can be easily resolved intoindividual stars. A galaxy dominated by an old population provides a clear viewof ancient processes of galaxy formation unimpeded by overlying youngerpopulations. By using spectroscopic metallicities of RGB stars in combinationwith our deep Main Sequence Turn-Off photometry we can constrain the ages ofdifferent stellar populations with particular accuracy. We find that the knownmetallicity gradient in Sculptor is well matched to an age gradient. This isthe first time that this link with age has been directly quantified. Thisgradient has been previously observed as a variation in Horizontal Branchproperties and is now confirmed to exist for Main Sequence Turn-Offs as well.It is likely the Sculptor dSph first formed an extended metal-poor populationat the oldest times, and subsequent more metal-rich, younger stars were formedmore towards the centre until the gas was depleted or lost roughly 7 Gyr ago.The fact that these clear radial gradients have been preserved up to thepresent day is consistent with the apparent lack of signs of recent tidalinteractions.

Deep Wide-Field Imaging down to the oldest Main Sequence Turnoffs in the Sculptor dwarf spheroidal galaxy