Abstract. ESO 338-IG04, also known as Tololo 1924-416, is a well known luminous blue compact galaxy in the local universe. Images obtained with the Hubble Space Telescope (HST) have shown that the central starburst region is composed of numerous bright point sources -young star clusters, surrounded by a population of old and intermediate age globular clusters. In this paper we use Ultra-Violet (UV) and optical HST photometry in five bands, and an extensive set of spectral evolutionary synthesis scenarios to investigate the age and masses of 124 star clusters. The very small reddening makes ESO 338-IG04 an excellent laboratory for studying the formation of such objects. We find that a careful treatment of the nebular emission component is crucial when modelling the broad-band colours of young starburst regions. We have used the star clusters to trace the temporal and spatial evolution of the starburst, and to put constraints on the star formation activity over a cosmological time-scale. The present starburst has been active for about 40 Myr and shows evidence for propagating star formation and structures triggered by galactic winds. A standard Salpeter initial mass function (IMF) extending up to 120 M provides the best fit to the data, although a flatter IMF cannot be excluded. The compact star clusters provide 30−40% of the UV luminosity and star formation activity. We find no evidence for dust obscuration even among the youngest (<1 Myr) clusters, and we propose that this may be related to a short time-scale for destruction of dusty molecular clouds. Over a longer time-scale, we find evidence for previous cluster formation epochs -notably one a couple of Gyr ago. The fraction of the galaxy's stellar mass contained in compact star clusters is found to be several percent, which is an unusually high value. The intermediate age clusters show a flattened space distribution which agrees with the isophotal shape of the galaxy, whereas the oldest clusters seem to have a spherical distribution indicating that they formed prior to the rest of the galaxy.

No abstract

No abstract

Two important questions are connected to the evolutionary history of blue compact dwarf galaxies (BCDs): the triggering mechanism of the starburst and the properties of the precursor(s) and successor. The halos of many BCDs show red colours indicating that the host galaxy is in fact of early type. But where did the gas come from? Was it there from the start in a quiescent mode or was it fed by a merger with an intergalactic gas cloud or a gas-rich dwarf? Is there a general answer to this question or are there different families of BCDs? The BCDs generating most of the interest are those with low chemical abundances, typically 10% solar. The only plausible precursors in this case are metal-poor dis, LSBGs or pure HI clouds (e.g. Thuan & Seitzer 197, ApJ 231, 680). In a comparison between LSBGs and BCDs Taylor et al. (e.g. 1997, ApJ 480, 524; 1996, ApJS 107, 143) found an excess of HI rich companions in the environments of BCDs which they interpret as a support of tidal triggering. We have studied a few massive (~ 109Mʘ ) metal- poor blue compact galaxies (BCGs). These are too bright to be classified as dwarfs but define an extension of the BCD family. For simplicity we will in the following use the common abbrevation BCD. In a search for possible precursors we have studied a sample of blue LSBGs with metallicities similar to BCDs (5-15%).

No abstract