the middle panel for the same example of HSBGs as in Fig. \[Fig2\]) and the histogram distributions of the derived ages of the galaxies (the right panel, where the shaded region is for LSBGs and the dashed-line is for HSBGs). The right panel also shows that the ages of most of the LSBGs are 1-5 Gyr with median (mean) value of 2.06 (2.18) Gyr, which means that the majority of their stars were formed quite recently. However, about 2% of the LSBGs have larger ages, 5-8 Gyr, which mean that they could form their stars at earlier time. Similarly, the ages of most of HSBGs are also 1-5 Gyr with the median value of 1.86 (mean as 1.92). About 3% of them have larger ages with 5-8 Gyr. This similarity may mean that the LSBGs and HSBGs have no much different star formation history, but the HSBGs are 0.2 Gyr younger than the LSBGs generally. All these results are consistent with those obtained with constant dust extinction, although the varying $A_V$ results in a bit older age ($\sim$0.4 Gyr) than the constant one. [The corresponding ages are also presented in Table \[tab1\].]{}

![The fitting results with PEGASE model and varying 