Abstract details

ULIRGs are supposed to trace intense starbursts from merging of galaxies. From the evolutionary synthesis of the optical to infrared ULIRG SEDs with PEGASE.3, we find the emission of grains heated by the starburst contribution is insufficient to fit the mid-IR excess. Other dust properties are considered. As submitted in Rocca-Volmerange et al, 2006, we then analyze the population of ULIRGs in the ISO-ESS deep survey at 12mu, comparable to the GTO deep survey, and in the 24mu SPITZER surveys. The typical bump observed at ~0.3mJy in the 12mu and 24mu faint counts is interpreted with the evolution of this ULIRG population instead of normal evolved galaxies. The role and nature of ULIRGs at high-redshifts are derived from this analysis. Finally we conclude on the role of stellar masses to trace the evolution of galaxies at the highest redshifts.