Dynamical consequences of CDM merger trees

Within the context of the standard structure formation scenario, massive present-day elliptical galaxies are sometimes thought of as the result of a major merger of spiral systems. Through extensive smooth particle hydrodynamic (SPH) simulations of merging spirals, we have explored these processes with the aim of quantifying their relaxation times. This is important, as it sets a minimum time interval between the onset of a merger and the appearance of an elliptical galaxy. We then compare this constraint with predictions of the hierarchical scenario, computed through Press-Schechter merger trees. We find evidence for elliptical systems that appear not to have been formed by a major merger of spirals.