Normal galaxies
In integrated galaxy spectra, the transition from star dominated emission to interestellar dust reradiation occurs at mid IR.
ISO studies of Mid IR colors in Virgo and Coma galaxies (Boselli et al 1997, 1998) ?
- PAH bands ubiquitous in the interstellar dust, destroyed by strong UV fields.
- Small grain emission related to UV radiation field
- Large grain emission proportional to interstellar radiation field
ISO detects hot dust in the nucleus of early type galaxies (Madden et al 1999).
Understanding mid IR integrated emission in local galaxies is crucial for studies in more distant objects.