High Resolution Radio and Optical Observations of the Central Starburst
  in the Low-Metallicity Dwarf Galaxy II Zw 40
  The extent to which star formation varies in galaxies with low masses, low
metallicities, and high star formation rate surface densities is not
well-constrained. To gain insight into star formation under these physical
conditions, this paper estimates the ionizing photon fluxes, masses, and ages
for young massive clusters in the central region of II Zw 40 -- the
prototypical low-metallicity dwarf starburst galaxy -- from radio continuum and
optical observations. Discrete, cluster-sized sources only account for half the
total radio continuum emission; the remainder is diffuse. The young (<5 Myr)
central burst has a star formation rate surface density that significantly
exceeds that of the Milky Way. Three of the 13 sources have ionizing photon
fluxes (and thus masses) greater than R136 in 30 Doradus. Although isolating
the effects of galaxy mass and metallicity is difficult, the HII region
luminosity function and the internal extinction in the center of II Zw 40
appear to be primarily driven by a merger-related starburst. The relatively
flat HII region luminosity function may be the result of an increase in ISM
pressure during the merger and the internal extinction is similar to that
generated by the clumpy and porous dust in other starburst galaxies.
