Collision-induced galaxy formation: semi-analytical model and multiwavelength predictions

A semi-analytical model is proposed that couples the Press-Schechter formalism for the number of galaxies with a prescription for galaxy-galaxy interactions that enables us to follow the evolution of galaxy morphologies along the Hubble sequence. Within this framework, we calculate the chemo-spectrophotometric evolution of galaxies to obtain spectral energy distributions. We find that such an approach is very successful in reproducing the statistical properties of galaxies as well as their time evolution. We are able to make predictions as a function of galaxy type. For clarity, we restrict ourselves to two categories of galaxies: early and late types that are identified with ellipticals and discs. In our model, irregulars are simply an early stage of galaxy formation. In particular, we obtain good matches for the galaxy counts and redshift distributions of sources from ultraviolet to submillimetre wavelengths. We also reproduce the observed cosmic star formation history and the diffuse background radiation, and make predictions as to the epoch and wavelength at which the dust-shrouded star formation of spheroids begins to dominate over the star formation that occurs more quiescently in discs. A new prediction of our model is a rise in the far-infrared luminosity density with increasing redshift, peaking at about zsimilar to3, and with a ratio to the local luminosity density rho(L ,nu)(z=z(peak))/rho(L ,nu) (z=0) about 10 times higher than that in the blue (B band) which peaks near zsimilar to2.