In the search for tidal structure in Galactic satellite systems, we have conducted a photometric survey over a 10 deg2 area centred on the Fornax dSph galaxy. The survey was made in two colours, and the resulting colour–magnitude data were used as a mask to select candidate Fornax RGB stars, thereby increasing the contrast of Fornax stars to background sources in the outer regions. Previously, we reported the presence of a shell (age 2 Gyr) located towards the centre of Fornax. In this contribution we reveal a second shell, significantly larger than the first, located 1.3° north-west from the centre of Fornax, outside the nominal tidal radius. Moreover, the distribution of Fornax RGB stars reveals two lobes extending to the spatial limit of our survey, and aligned with the minor axis and with the two shells. These results support the hypothesis of a merger between Fornax and a gas-rich companion approximately 2 Gyr ago.

The Fornax dSph is an interesting case as it contains five old globular clusters and its field stars, although predominantly of intermediate (3-8 Gyr old) age, cover a wide range of age and metallicity. Detailed abundance analysis is crucial to our understanding of the earliest star formation epoches, where classic CMD analysis fails to provide a unique answer. It also allows us to measure the chemical evolution of the stellar population following tracers of different enrichment mechanisms through time, e.g. SN type II (alpha elements); AGB stars (s-process elements) etc. With our large sample of abundance measurements we will obtain a detailed picture of the evolution of Fornax and of the role played by small galaxies in the building up of larger ones.