Multiwavelength study of nearly face-on low surface brightness disk galaxies

We study the ages of a large sample (1,802) of nearly face-on disk low surface brightness galaxies (LSBGs) by using the evolutionary population synthesis (EPS) model PEGASE with exponential decreasing star formation rate to fit their multiwavelength spectral energy distributions (SEDs) from far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1-5 Gyr for most of the sample no matter the constant or varying dust extinction is adopted, which are similar to most of the previous studies on smaller samples. This means that these LSBGs formed their majority of stars quite recently. However, a small part of the sample (~2-3%) have larger ages as 5-8 Gyr, meaning their major star forming process may occur earlier. At the same time, a large sample (5,886) of high surface brightness galaxies (HSBGs) are selected and studied in the same method for comparisons. The derived ages are 1-5 Gyr for most of the sample (97%) as well. These may mean that probably these LSBGs have no much different star formation history from their HSBGs counterparts. But we should notice that the HSBGs are about 0.2 Gyr younger generally, which could mean that the HSBGs may have more recent star forming activities than the LSBGs.