Involved people at OAB: Greggio.
Within the class of dwarf galaxies, the Blue Compact Dwarf (BCD) appear dominated by a recent burst of star formation, which causes their extremely blue colors. It has been proposed that some of these galaxies (the lowest metallicity ones) there are truly young objects, experiencing their very first star formation episode. It has also been proposed that BCDs represent an evolutionary stage of the general class of dwarf galaxies, a stage in which a strong ongoing star formation activity promotes galactic winds which transform a (gas rich) dwarf irregular into a (gas poor) dwarf spheroidal. Finally, BCDs could be the class of objects responsible for the excess faint blue counts described in the previous section. In collaboration with R. Schulte-Ladbeck (Univ. of Pittsburg) and U. Hopp (Univ. of Munich) we are investigating in detail the stellar content of a sample of 5 BCD galaxies for which we have HST photometry proprietary data. By applying the synthetic color-magnitude diagram (CMD) method, we derive the quantitative SF history in these galaxies, which will allow us to properly locate these objects in an evolutionary scenario.
In 1999 we have completed the study of the infrared CMD of VIIZw403, for which we also had optical HST data. This allowed us to calibrate the infrared magnitude of the tip of the red giant branch as a distance indicator [Schulte-Ladbeck et al. (1999)]. We also studied the infrared CMD of Mrk 178 [Schulte-Ladbeck, Hopp, Greggio and Crone (2000), AJ submitted], and are currently investigating the CMD of the third galaxy in the sample (IZw36). We plan to complete the quantitative analysis of the whole sample within the next two years. We will then be able to address the issue of the mutual relations of BCDs to the other kinds of dwarfs, as well as to derive clues for the interpretation of the evolution of the galaxy population on cosmological time scales.