Shocked molecular hydrogen in NGC 4038/4039, 'the antennae'

The nuclei of the interacting pair NGC 4038/4039 have been observed in the 2.123-micron v = 1 to 0 S(1) line of excited molecular hydrogen. The observed S(1)-line luminosity/FIR luminosity ratios for NGC 4038 and NGC 4039 are found to be too high to be compatible with a model in which the H2 is excited by radiatively driven gas motions in the star-forming regions. Alternative excitation mechanisms considered include supernova explosions and collisions between the molecular clouds of the two galaxies. 49 refs.