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The analysis of the early star formation history (SFH) of nearby galaxies,obtained from their resolved stellar populations is relevant as a test forcosmological models. However, the early time resolution of observationallyderived SFHs is limited by several factors. Thus, direct comparison ofobservationally derived SFHs with those derived from theoretical models ofgalaxy formation is potentially biased. Here we investigate and quantify thiseffect. For this purpose, we analyze the duration of the early star formationactivity in a sample of four Local Group dwarf galaxies and test whether theyare consistent with being true fossils of the pre-reionization era; i.e., ifthe quenching of their star formation occurred before cosmic reionization by UVphotons 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. Accountingfor time resolution effects, the SFHs peak as much as 1.25 Gyr earlier than theoptimal solutions. Thus, this effect is important for a proper comparison ofmodel and observed SFHs. It is also shown that none of the analyzed galaxiescan be considered a true-fossil of the pre-reionization era, although it ispossible that the {\it outer regions} of Cetus and Tucana are consistent withquenching by reionization.

The ACS LCID Project XI. On the early time resolution of LG dwarf galaxy SFHs: Comparing the effects of reionization in models with observations