Population synthesis for the spectra of blue compact dwarf galaxies

In order to study the history of star formation, energy source and internal dust distribution in blue compact dwarf galaxies (BCDGs), we have compared the observed spectra of the nuclei of 7 BCDGs with the predictions of stellar population synthesis model. The results suggest that BCDGs are old galaxies, in which star formation occur in short intense bursts separated by long quiescent phases. The star formation rate was very high during 5 x 10(7)similar to 10(9) yr, but has now decreased. We find that the main energy source of BCDGs comes from young, massive stars. We have derived the internal reddening that affects the nuclear stellar population by tie population synthesis method and the internal reddening of the emitting gas clouds from the Balmer line ratio and found the former to be consistently and significantly smaller than the latter. This feature can be explained by a model of foreground dust clumps with different covering factors for the gas and stars. Finally, based on the stellar population of BCGs (blue compact galaxies) and BCDGs, we suggest a detailed evolutionary link among different dwarf galaxies.