a galaxy (Li et al. 2004a,b).

In our fitting analysis, the internal dust extinctions are considered in two methods, the constant A$_V$ (0.6 for LSBGs and 0.8 for HSBGs) and varying $A_V$ within A$_V$ = 0.1 - 1.6. A zero initial metallicity of interstellar medium (ISM) is taken. We adopt the exponential decreasing SFR ([*SFR(t)*]{} $\propto$ [*e*]{}$^{-t/\tau}$) with $\tau$ = 0.1 - 15 Gyr varying in the fittings. The IMF is assumed to follow the Salpeter (1955) form, $\Phi$(M) = A$\times$ $M^{-\alpha}$ with ${\alpha}$ = 2.35 and a lower cutoff of $M_{l}$ = 0.1 $M_{\odot}$ and an upper cutoff $M_{u}$ = 125 M$_{\odot}$(Sawicki & Yee 1998). As a result, a rest-frame modeled spectra with various star formation histories are generated by running the PEGASE code.

Model Fits And Results
======================

We present the fitting method in Sect. \[sect:analysis0\], and the fitting results in Sects. \[sect:analysis1\], \[sect:analysis2\]. Extinction affects intrinsic colors of the objects and hence accurate ages, so the photometric measurements must be dereddened before running the fitting procedure. We use two methods for considering the internal dust extinction of the galaxies in fitting procedures, the constant and varying $A_V$.

The fitting method {#sect:analysis0}
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To estimate the ages of 