THE DARK SIDE OF STAR-FORMATION IN THE ANTENNAE GALAXIES

We compare mid-infrared images of the Antennae galaxies (NGC 4038/39) from the Infrared Space Observatory, with optical images from the Hubb le Space Telescope. The midinfrared observations show that the most in tense starburst in this colliding system of galaxies takes place in an off-nucleus region that is inconspicuous at optical wavelengths. The analyses of the mid-infrared spectra indicate that the most massive st ars are being formed in an optically obscured knot of 50 pc radius, wh ich produces about 15% of the total luminosity from the Antennae galax ies between 12.5 mu m and 18 mu m. The mid-infrared observations repor ted here demonstrate that the interpretation of star formation propert ies in colliding/merging systems based on visible wavelengths alone ca n be profoundly biased due to dust obscuration. The multiwavelength vi ew of this nearby prototype merging system suggests caution in derivin g scenarios of early evolution of high redshift galaxies using only ob servations in the narrow rest-frame ultraviolet wavelength range.