Star-forming regions in blue compact dwarf galaxies

We present near-infrared 2.1-μm continuum and Brγ and 1–0S(1) line images of three blue compact dwarf galaxies: II Zw 40, NGC 5253 and 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 Brγ and weak diffuse H₂ emission, indicating the presence of one or more compact nuclei, and also tidal tails. We consider the possible origins of the H₂ emission, and conclude that shock excitation in cloud collisions, and hence dynamical processes such as interactions or mergers, is important. By comparing models of the equivalent width of Brγ 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 current 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 differences between those in NGC 5253. We compare the masses and sizes of the star formation sites to those of present-day globular clusters.