GRAPE-SPH chemodynamical simulation of elliptical galaxies - II : Scaling relations and the fundamental plane

Abstract

We simulate the formation and chemodynamical evolution of 128 elliptical galaxies using a GRAPE-SPH code that includes various physical processes that are associated with the fort-nation of stellar systems: radiative cooling, star formation, feedback from Type 11 and la supernovae and stellar winds, and chemical enrichment. We find that the star formation time-scale controls when and where stars form in the contracting gas cloud, determines the effective radius at given mass, and is constrained by observation to be 10 times longer than the local dynamical time-scale. We succeed in reproducing the observed global scaling relations under our cold dark matter based scenario, e.g. the Faber-Jackson relation, the Kormendy relation and the fundamental plane. An intrinsic scatter exists along the fundamental plane, and the origin of this scatter lies in differences in merging history. Galaxies that undergo major merger events tend to have larger effective radii and fainter surface brightnesses, which result in larger masses, smaller surface brightnesses and larger mass-to-light ratios. We can also reproduce the observed colour-magnitude and mass-metallicity relations, although the scatter is larger than observed. The scatter arises because feedback is not very effective and star formation does not terminate completely in our simulations. similar to 25 per cent of accreted baryons are blown away in the simulations, independent of the assumed star formation time-scale and initial mass function. Most heavy elements end up locked into stars in the galaxy. The ejected metal fraction depends only on the star formation time-scale, and is similar to 2 per cent even to rapid star formation.