Evolution of starbursts and AGN: Future SPICA observations

We discuss the potential of high sensitivity mid-IR and far-IR spectroscopy to derive the physical properties of active nuclei and starburst regions of local and distant galaxies. For local galaxies, it will be possible to map the discs and the interstellar medium through the low ionization ionic lines and a variety of molecular tracers, such as OH, H2O and high-J CO. At increasing distance, most of the ionic nebular lines (typical of stars and active galactic nuclei) are shifted into the far-IR, making possible to compare the spectra observed in high redshift galaxies with those predicted by different evolutionary scenarios. At the very high redshift of 10-15, sensitive mid-to-far-IR spectrometers, such as those planned to be at the focal plane of the future SPICA mission, could be adequate to detect the H recombination lines excited in the HII regions around population III stars, if these stars happened to reside in large clusters of more than 105 members.