UCLA

Infrared photometry and later infrared spectroscopy provided powerful diagnostics to distinguish between the main emission mechanisms in galaxies: AGN and Starburst. After the pioneering work on infrared photometry with IRAS in the far-IR and the San Pedro Martir and ESO ground-based work in the near-IR, ISO photometry extended up to 200 μm the coverage of the galaxies energy distributions. Then Spitzer collected accurate mid-infrared spectroscopy on different samples of galaxies. We will review the work done on the 12 μm galaxy sample since the times of IRAS photometry to the new Spitzer spectroscopy. The main results on the multifrequency data of 12 μm selected Seyfert galaxies are presented and discussed in the light of unification and evolution models. The spectroscopic work of Spitzer will soon be complemented at longer wavelengths by the Herschel spectrometers and in the future by SPICA at higher redshift. © 2010: Instituto de Astronomía, UNAM.