we should notice the fact that the HSBGs are slightly younger than the LSBGs, $\sim$0.2 Gyr shown by the median (mean) ages of the samples. [The median (mean) ages of the sample galaxies are presented in Table \[tab1\].]{}

![The fitting results with PEGASE model and constant dust extinction ($A_V$=0.6 for LSBGs and $A_V$=0.8 for HSBGs) for our sample galaxies. The left panel shows the SED fitting for one example of LSBGs (RA=8.06543, DEC=0.90616 in 2000 epoch, the derived age is 1.57 Gyr), the middle panel shows the SED fitting for one example of HSBGs (RA=6.75941, DEC=-9.63505 in 2000 epoch, the derived age is 1.44 Gyr)), and the right panel shows the histogram distributions of the derived ages of LSBGs (shade region) and HSBGs (dashed-line) with bin of 0.2 Gyr. []{data-label="Fig2"}](ms471fig2a.eps "fig:"){width="4.8cm" height="4.8cm"} ![The fitting results with PEGASE model and constant dust extinction ($A_V$=0.6 for LSBGs and $A_V$=0.8 for HSBGs) for our sample galaxies. The left panel shows the SED fitting for one example of LSBGs (RA=8.06543, DEC=0.90616 in 2000 epoch, the derived age is 1.57 Gyr), the middle panel shows the SED fitting for one example of HSBGs (RA=6.75941, DEC=-9.63505 in 2000 epoch, the derived age is 1.44 Gyr)), and 