We present deep photometry in the B , V and I filters from CTIO/MOSAIC for about 270.000 stars in the Fornax dwarf Spheroidal galaxy , out to a radius of r _ { ell } \approx 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 - 10 Gyr ) stellar populations , but also includes ancient ( 10 - 14 Gyr ) , and young ( \leq 1 Gyr ) 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 1.9 kpc from the centre , a total mass in stars of 4.3 \times 10 ^ { 7 } M _ { \odot } was formed , from the earliest times until 250 Myr 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 ] \leq - 2.5 dex to [ Fe/H ] = - 1.5 dex between 8 - 12 Gyr ago , after which a more gradual enrichment resulted in a narrow , well-defined sequence which reaches [ Fe/H ] \approx - 0.8 dex , \approx 3 Gyr 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 ] \geq - 1.5 dex , with a clear trend in age .