The star formation histories of red and blue low surface brightness disk galaxies

Aims. We study the star formation histories (SFH) and stellar populations of 213 red and 226 blue nearly face-on low surface brightness disk galaxies (LSBGs), which are selected from the main galaxy sample of Sloan Digital Sky Survey (SDSS) Data Release Seven (DR7). We also compare the stellar populations and SFH between the two groups. Methods. The sample of both red and blue LSBGs have sufficient signal-to-noise ratio in the spectral continua. We obtain their absorption-line indices (e.g. Mg-2, H delta(A)), D-n(4000) and stellar masses from the MPA/JHU catalogs to study their stellar populations and SFH. Moreover we fit their optical spectra (stellar absorption lines and continua) by using the spectral synthesis code STARLIGHT on the basis of the templates of simple stellar populations (SSPs). Results. We find that red LSBGs tend to be relatively older, of higher metallicity, are more massive and have a higher surface mass density than blue LSBGs. The D-n(4000)-H delta(A) plane shows that perhaps red and blue LSBGs have different SFH: blue LSBGs are more likely to experience a sporadic star formation event now, whereas red LSBGs are more likely to have formed stars continuously over the past 1-2 Gyr. Moreover, the fraction of galaxies that experienced recent sporadic formation events decreases with increasing stellar mass. Furthermore, two sub-samples are defined for both red and blue LSBGs: the sub-sample within the same stellar mass range of 9.5 = log(M-star/M-circle dot) <= 10.3, and the surface brightness limiting sub-sample with mu(0)(R) >= 20.7 mag arcsec(-2). They show consistent results with the total sample in the corresponding relationships, which confirm that our results of the comparasion of the blue and red LSBGs are robust.