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 outer regions of Cetus and Tucana are consistent with quenching by reionization .