Ionized Gas Kinematics at High Resolution. II: Discovery of a Double
  Infrared Cluster in II Zw 40
  The nearby dwarf galaxy II Zw 40 hosts an intense starburst. At the center of
the starburst is a bright compact radio and infrared source, thought to be a
giant dense HII region containing ~14,000 O stars. Radio continuum images
suggest that the compact source is actually a collection of several smaller
emission regions. We accordingly use the kinematics of the ionized gas to probe
the structure of the radio-infrared emission region. With TEXES on the
NASA-IRTF we measured the 10.5um [SIV] emission line with effective spectral
resolutions, including thermal broadening, of ~25 and ~3 km/s and spatial
resolution ~1". The line profile shows two distinct, spatially coextensive,
emission features. The stronger feature is at galactic velocity and has FWHM 47
km/s. The second feature is ~44km/s redward of the first and has FWHM 32 km/s.
We argue that these are two giant embedded clusters, and estimate their masses
to be ~3x10^5Mo and ~1.5x10^5 Mo. The velocity shift is unexpectedly large for
such a small spatial offset. We suggest that it may arise in a previously
undetected kinematic feature remaining from the violent merger that formed the
galaxy.
