The temporal and spatial evolution of the starburst in ESO 338-IG04 as probed by its star clusters

Abstract

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 in the luminous blue compact galaxy ESO338-IG04 (Tololo 1924-416). The very small internal reddening makes ESO 338-IG04 an excellent laboratory for studying the formation of massive star clusters. 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. A standard Salpeter initial mass function (IMF) extending up to 120 solar masses provides the best fit to the data, although a flatter IMF cannot be excluded. The compact star clusters provide 30-40 percent of the UV luminosity and star formation activity. We find no evidence for dust obscuration even among the youngest (< 1 Myr) clusters. The fraction of 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.(abridged)