STAR-FORMING REGIONS IN BLUE COMPACT DWARF GALAXIES

We present near-infrared 2.1-mu m continuum and Br gamma and 1-OS(1) l ine images of three blue compact dwarf galaxies: II Zw 40, NGC 5253 an d He 2-10. Comparison of the morphologies of the emission-line regions and continuum together with the line ratios shows that in these cases the starbursts are typified by strongly peaked Br gamma and weak diff use H-2 emission, indicating the presence of one or more compact nucle i, and also tidal tails. We consider the possible origins of the H-2 e mission, and conclude that shock excitation in cloud collisions, and h ence dynamical processes such as interactions or mergers, is important . By comparing models of the equivalent width of Br gamma to other age constraints from the literature we show that the star formation must have occurred not only recently but in a short-duration burst. The cur rent centres of star formation in all three galaxies are of a similar age but, whereas the hotspots in He 2-10 are coeval, we find phase dif ferences between those in NGC 5253. We compare the masses and sizes of the star formation sites to those of present-day globular clusters.