C. Cesarsky on "The role of LIRGS in galaxu evolution"

I shortly mentioned (U)LIRGS being associated with mergers before. They are very bright in the near and far-infrared and dust emission plays a major role here. Indeed, they must have been much more usual in the earlier universe, since the IR-background which is weak in the local universe, but reaches or even succeeds the optical background radiation at higher redshifts.

By counting galaxies in different wavelengths and at different z, one can determine how the galaxy population has changed over cosmic time. A strong evolution is found and LIRGS are found to be frequent enough to account for all of the IR-background radiation.

Not all of them are irregular: 36% of LIRGS are instead found to be disk-like galaxies. At the rate that LIRGS are forming stars, they would double their mass (in stars) in less than 1 Gyr. But they only do this temporarily (for about 100 Myr) in the LIRG phase. This phase can reoccur and each time about 5-10% of the stellar mass is added.

Catherine Cesarsky, by the way, is the director general of ESO.