EVOLUTION OF SYSTEMS OF GALAXIES IN COLD DARK-MATTER MODELS

We study the evolution of groups and clusters of galaxies in a OMEGA = 1, h = 0.5, LAMBDA = 0, CDM scenario using numerical simulations norm alized to deltaM/M = 1. We construct models for galaxy formation assum ing instantaneous cooling of gas and the related formation of galaxies in local high-density regions. We compute models that inhibited galax y formation when the corresponding galactic halo is embedded in a grea ter cloud for which its cooling time exceeds its crossing time. In the se models we find a significant reduction of galaxy formation efficien cy in large galactic systems. Mergers of galaxies are taken into accou nt using suitable cross sections and a binding energy criterion. We fi nd that about approximately 10% of the galaxies have undergone mergers at the present time. We have implemented simple models that consider the effects of energy input by supernovae winds. We find that these ef fects provide a successful fit to the observed Tully-Fisher relation. We have considered gas infall in systems of galaxies and the effects o f supernova winds in the intracluster medium in order to account for t he observed gas-to-stars mass ratio M(gas)/M(stars) as a function of t emperature. Although we find a negligible amount of gas infall (<10%), the models allow significant gas mass loss due to supernova winds in small clusters which would explain their high observed galaxy formatio n efficiency. We have analyzed the spatial distribution of galaxies an d their peculiar velocity field in the models. Only when a moderate su ppression of galaxy formation in dense environments is considered, is the galaxy-galaxy spatial correlation function consistent with observa tions. We find no significant velocity bias of the galaxies with respe ct to the dark matter in any model. This results suggest that the obse rved galaxy peculiar velocity field put strong constraints to the ampl itude of the primordial mass fluctuations in the cosmological models.