Cosmic star formation: constraints on the galaxy formation models

We study the evolution of the cosmic star formation in the Universe by computing the luminosity density (in the UV, B, J and K bands) and the mass density of galaxies in two reference models of galaxy evolution: the pure-luminosity evolution (PLE) model developed by Calura & Matteucci and the semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al. The former includes a detailed description of the chemical evolution of galaxies of different morphological types; it does not include any number evolution of galaxies whose number density is normalized to the observed local value. On the other hand, the SAM includes a strong density evolution following the formation and the merging histories of the DM haloes hosting the galaxies, as predicted by the hierarchical clustering scenario, but it does not contain morphological classification or chemical evolution. Our results suggest that at low-intermediate redshifts (z < 1.5) both models are consistent with the available data on the luminosity density of galaxies in all the considered bands. At high redshift the luminosity densities predicted in the PLE model show a peak due to the formation of ellipticals, whereas in the hierarchical picture a gradual decrease of the star formation and of the luminosity densities is predicted for z > 2.5. At such redshifts the PLE predictions tend to overestimate the present data in the B band, whereas the SAM tends to underestimate the observed UV luminosity density. As for the stellar mass density, the PLE picture predicts that nearly 50 and 85 per cent of the present stellar mass is in place at z similar to 4 and z similar to 1, respectively. According to the hierarchical SAM, 50 and 60 per cent of the present stellar mass is completed at z similar to 1.2 and z = 1, respectively. Both predictions fit the observed stellar mass density evolution up to z = 1. At z > 1, the PLE model and SAM tend to overestimate and underestimate the observed values, respectively. We discuss the origin of the similarities and of the discrepancies between the two models, and the role of observational uncertainties (such as dust extinction) in comparing models with observations.