On the origin of early-type galaxies and the evolution of the interaction rate in the field

Using cosmological N-body simulations of critical and open cold dark matter (CDM) models, we have identified galaxy-sized dark matter halos originated by major binary mergers. Remnants of major merging events between redshift z = 1 and the present have typically not yet been accreted into groups and clusters, and hence they can be linked to bright early-type field galaxies . The rate of formation of binary merger remnants is 1.9 x 10(-13)(1 + z)(3 .1 +/- 0.2) and 1.6 x 10(-14)(1 + z)(2.5) (+/- 0.4) h(3) Mpc(-3) yr(-1) for a critical tilted CDM and an open CDM model, respectively. The average age of these merger remnants is about 6 Gyr, 40% of the age of the universe. I n an open universe, field early-type galaxies formed at z < 1 by major merg ers would account for only similar to 5% of the total population of early-t ype galaxies. This fraction is much higher (similar to 55%) in critical mod els. These results are discussed together with present observational constr aints.