IR spectroscopy in the range 12-230 micron with the SPace IR telescope for
Cosmology and Astrophysics (SPICA) will reveal the physical processes that
govern the formation and evolution of galaxies and black holes through cosmic
time, bridging the gap between the James Webb Space Telescope (JWST) and the
new generation of Extremely Large Telescopes (ELTs) at shorter wavelengths and
the Atacama Large Millimeter Array (ALMA) at longer wavelengths. SPICA, with
its 2.5-m telescope actively-cooled to below 8K, will obtain the first
spectroscopic determination, in the mid-IR rest-frame, of both the
star-formation rate and black hole accretion rate histories of galaxies,
reaching lookback times of 12 Gyr, for large statistically significant samples.
Densities, temperatures, radiation fields and gas-phase metallicities will be
measured in dust-obscured galaxies and active galactic nuclei (AGN), sampling a
large range in mass and luminosity, from faint local dwarf galaxies to luminous
quasars in the distant Universe. AGN and starburst feedback and feeding
mechanisms in distant galaxies will be uncovered through detailed measurements
of molecular and atomic line profiles. SPICA's large-area deep
spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for
unbiased samples of tens of thousands of galaxies, out to redshifts of z~6.
Furthermore, SPICA spectroscopy will uncover the most luminous galaxies in the
first few hundred million years of the Universe, through their characteristic
dust and molecular hydrogen features.