The Star Formation & Chemical Evolution History of the Fornax Dwarf
  Spheroidal Galaxy
  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\sim0.8 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 (<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 4.3x10^7 Msun 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]<-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]\sim-0.8 dex, \sim3 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]>-1.5
dex, with a clear trend in age.
