  Imaging of the Antennae galaxies (NGC 4038/4039) with the Infrared Array
Camera (IRAC) aboard the Spitzer Space Telescope reveals large concentrations
of star forming activity away from both nuclei of the two merging galaxies.
These images confirm earlier findings based on ISO data with lower angular
resolution. The short wavelength emission shows numerous compact sources
identified as stellar clusters. At the longer wavelengths, bright, more
amorphous and filamentary features correlate well with the known distributions
of denser gas, warm dust, and HII regions. There are also fainter, more diffuse
components at all wavelengths that permeate the entire region and extend into
the two tidal tails. Non-stellar dust emission dominates the 5.8 and 8.0 micron
images, accounting for as much as 79% of the light at 5.8 micron and 95% at 8
micron, averaged over the entire galaxy. Assuming that the non-stellar emission
traces star formation, the IRAC data provide a view into the total underlying
star forming activities unaffected by obscuration. Using the flux ratio of
non-stellar to stellar emission as a guide, we map the local star formation
rate in the Antennae and compare that to similar measurements in both normal
and infrared-luminous galaxies. This rate in the active regions is found to be
as high as those seen in starburst and some ultra-luminous infrared galaxies on
``per unit mass'' basis. The two galactic centers actually have lower star
forming rates than the off-nuclear regions despite the presence of abundant
dense gas and dust, suggesting that the latter is a necessary but not
sufficient condition for on-going star formation.
