V. Charmandaris 1, O. Laurent 2, F. Mirabel 1, & P. Gallais 1
1 DEMIRM, Observatoire de Paris, FRANCE
2 DSM/DAPNIA/SAp, CEA-Saclay, 91191 Gif sur Yvette Cedex FRANCE
Galaxy interactions, used as ``cosmic experiments'', provide an ideal laboratory for the study of star formation. Tidal effects cause major redistribution of the interstellar gas of the interacting galaxies leading to the formation of large scale star-forming complexes, over regions where the gas and dust density as well as the intensity of the radiation field vary substantially.
A sample of nearby interacting galaxies has been observed in the mid-IR by ISOCAM as part of the GT program CAMACTIV (P.I. F.Mirabel). Here we present mid-IR images and spectra on four systems for which not only a wealth of multi-wavelength observations already exist but also the dynamical history of the interaction is fairly well understood. These include ``The mice'' (NGC4676) and three collisional ring galaxies: the Cartwheel, Arp 118, and Arp 10. The dynamics of the Cartwheel and NGC4676 have been successfully modeled numerically while Arp118 whose H2 and HI gas distribution has been mapped in detail also harbors a Seyfert nucleus. Arp10 on the other hand is known to exhibits a ``threshold'' variation in the star formation rate along its ring.
The recent study of the well known ``Antennae'' galaxy (NGC4038/39) has indicated that collisionally induced star forming regions heat the gas and dust in the interstellar medium of those galaxies producing a rich mid-IR spectrum. Using a series of mid-IR color diagnostics we developed based on all galaxies of our CAMACTIV sample we present a new insight to the physical mechanisms which control the morphology and structure of the ISM in these four galaxies.