2002AJ....124.2516B

We report subarcsecond-resolution Very Large Array and Keck mid-infrared imaging of the dwarf starburst galaxy II Zw 40. II Zw 40 contains a bright compact thermal radio and infrared source with all the characteristics of a collection of dense H II regions ionized by at least 14,000 O stars. The supernebula is revealed to consist of multiple sources within an envelope of weaker emission. The radio emission is dominated by free-free emission at 2 cm, and the spectrum of this emission appears to be rising. This suggests that the free-free emission is optically thick at 2 cm and that the individual H II regions are ∼1 pc in size. This complex of ``supernebulae'' dominates the total infrared luminosity of II Zw 40, although the radio source is less than ∼150 pc in diameter. Multiple super-star clusters appear to be forming here, the much larger analogs of large Galactic H II region complexes.