Hot Dust in Interacting Galaxies: from ISO to SIRTF

I will present a review on the mid-IR (5--16 microns) spectral imaging of a sequence of nearby interacting galaxies, observed by ISOCAM. The galaxies are part of the well known Toomre's ``merger sequence'' which was defined as a sample of galaxies depicting progressive snapshots in the time evolution of a merging event. It will bee shown that the ratio of the 15 to 7 micron flux correlates well with the IRAS colors of the galaxies, and that using it in conjunction with the [NeII] and [NeIII] lines one can trace the intensity of the radiation field in a starburst. This suggests that even though the bolometric luminosity of merging luminous infrared galaxies is dominated by emission at wavelengths longer than 40 microns, the study of the mid-IR spectral energy distribution is a powerful tool in understanding their global star formation history. As a second step I will highlight the capabilities of the Infra-Red Spectrograph (IRS), and how it will enable us to improve some of the limitations of ISO. IRS provides a complete spectral coverage between 5 and 40 microns with a sensitivity ~10 times better than ISO, a spectral resolution ranging between 60 and 600 and a spatial resolution of nearly 1.5 arcsec. IRS is being built by Cornell Univ. and will be one of three instruments on board the Space Infrared Telescope Facility (SIRTF).