ISOCAM observations of galaxies

The current results of our ISOCAM Guaranteed Time observations of nearby galaxies demonstrate the wide variety of physical conditions and components that are present in mid infrared wavelengths. In the disks of normal galaxies, where the emission is dominated by the aromatic carbon particles, the mid-IR emission at 6 μm and 15 μm provides a useful star formation indicator, while the same is not true when the mid infrared emission is dominated by central HII regions, as in starburst galaxies. Early type galaxies show a variety of characteristics, from mostly photospheric emission to various degrees of dust emission, while some ellipticals are clearly dominated by strong non-thermal radio sources in the mid infrared. ISOCAM imaging spectroscopy provide strong and unique constraints on the nature of the infrared sources associated with luminous infrared galaxies.