2012A&A...544A..73D

We present deep photometry in the B, V and I filters from CTIO/MOSAIC for about 270000 stars in the Fornax dwarf spheroidal galaxy, out to a radius of r_ell≃0.8 degrees. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual red giant branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1-10Gyr) stellar populations, but also includes ancient (10-14Gyr), and young (≤1Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9kpc from the centre, a total mass in stars of 4.3x10⁷M_☉ was formed, from the earliest times until 250Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from [Fe/H]≤-2.5dex to [Fe/H]=-1.5dex between 8-12Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches [Fe/H]≃-0.8dex, ≃3Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in [Mg/Fe] is seen for the stars with [Fe/H]≥-1.5dex, with a clear trend in age.