SEMIANALYTIC MODELING OF GALAXY EVOLUTION IN THE IR SUBMM RANGE/

This paper proposes a new semi-analytic modelling of galaxy properties in the IRI submm wavelength range, which is explicitly set in a cosmo logical framework. We start from a description of the non-dissipative and dissipative collapses of primordial perturbations, and add star fo rmation, stellar evolution and feedback, as well as the absorption of starlight by dust and its re-emission in the IR and submm. This type o f approach has had some success in reproducing the optical properties of galaxies. We hereafter propose a simple extension to the IR/submm r ange. The growth of structures is followed according to the standard c old dark matter model. We assume that star formation proceeds either i n a 'quiescent' mode, e.g., as in discs, or in a 'burst' mode with 10 times shorter time-scales. In order to reproduce the current data on t he evolution of the comoving cosmic star formation rate and gas densit ies, we need to introduce a mass fraction involved in the 'burst' mode strongly increasing with redshift, probably reflecting the increase o f interaction and merging activity. We estimate the IR/submm luminosit ies of these 'mild starburst' and 'luminous UV/ IR galaxies', and we e xplore how much star formation could be hidden in heavily extinguished , 'ultraluminous IR galaxies' by designing a family of evolutionary sc enarios which are consistent with the current status of the 'cosmic co nstraints', as well as with the IRAS 60-mu m luminosity function and f aint counts, but with different high-z IR luminosity densities. Howeve r,these scenarios generate a cosmic infrared background whose spectrum falls within the +/-1 sigma range of the isotropic IR component detec ted by Puget et al. and revisited by Guiderdoni et al. We give predict ions for the faint galaxy counts and redshift distributions at IR and submm wavelengths. The submm range is very sensitive to the details of the evolutionary scenarios. As a result, the ongoing and forthcoming observations with ISO and SCUBA land later with SIRTF, SOFIA, FIRST an d PLANCK) will put strong constraints on the evolution of galaxies at z similar to 1 and beyond.