A new study of stellar substructures in the Fornax dwarf spheroidal
  galaxy
  Using deep V, B-V wide-field photometry, we have conducted a new study of
stellar over-densities in the Fornax dwarf spheroidal galaxy by determining
detailed Star Formation Histories from Colour-Magnitude Diagram analysis. We
have concentrated on the relatively young stellar component (<4 Gyr old), and
compared this to the underlying Fornax field population. We have studied in
more detail the previously known inner shell-like structure and shown that it
has a well-defined age-metallicity relation with a peak at ~1.5 Gyr,
[Fe/H]=-0.6 dex. Comparison to the Fornax centre shows that the over-dense
feature is consistent with the age-metallicity relation of young field stars,
and likely formed from Fornax gas. This is consistent with a scenario in which
the over-density was formed by the re-accretion of previously expelled gas. We
have also discovered a new stellar over-density, located 0.3 degrees (0.7 kpc)
from the centre, which is only 100 Myr old, with solar metallicity. This
feature constitutes some of the youngest, most metal-rich stars stars observed
in Fornax to date. It is unclear how the young over-density was formed,
although the age and metallicity of stars suggest this feature may represent
the last star formation activity of the Fornax dSph.
