The ACS LCID Project XI. On the early time resolution of LG dwarf galaxy
  SFHs: Comparing the effects of reionization in models with observations
  The analysis of the early star formation history (SFH) of nearby galaxies,
obtained from their resolved stellar populations is relevant as a test for
cosmological models. However, the early time resolution of observationally
derived SFHs is limited by several factors. Thus, direct comparison of
observationally derived SFHs with those derived from theoretical models of
galaxy formation is potentially biased. Here we investigate and quantify this
effect. For this purpose, we analyze the duration of the early star formation
activity in a sample of four Local Group dwarf galaxies and test whether they
are consistent with being true fossils of the pre-reionization era; i.e., if
the quenching of their star formation occurred before cosmic reionization by UV
photons was completed. Two classical dSph (Cetus and Tucana) and two dTrans
(LGS-3 and Phoenix) isolated galaxies with total stellar masses between
$1.3\times 10^6$ to $7.2\times 10^6$ M$_\odot$ have been studied. Accounting
for time resolution effects, the SFHs peak as much as 1.25 Gyr earlier than the
optimal solutions. Thus, this effect is important for a proper comparison of
model and observed SFHs. It is also shown that none of the analyzed galaxies
can be considered a true-fossil of the pre-reionization era, although it is
possible that the {\it outer regions} of Cetus and Tucana are consistent with
quenching by reionization.
