Clues on Regularity in the Structure and Kinematics of Elliptical Galaxies from Self-consistent Hydrodynamical Simulations: the Dynamical Fundamental Plane

Abstract

[Abridged] We have analysed the parameters characterising the mass, size and velocity dispersion both at the baryonic scale and at the halo scales of two samples of relaxed elliptical-like-objects (ELOs) identified, at z=0, in a set of self-consistent hydrodynamical simulations operating in the context of a concordance cosmological model. At the halo scale they have been found to satisfy virial relations; at the scale of the baryonic object the (logarithms of the) ELO stellar masses, projected stellar half-mass radii, and stellar central l.o.s. velocity dispersions define a flattened ellipsoid close to a plane (the intrinsic dynamical plane, IDP), tilted relative to the virial one, whose observational manifestation is the observed FP. The ELO samples have been found to show systematic trends with the mass scale in both, the relative content and the relative distributions of the baryonic and the dark mass ELO components, so that homology is broken in the spatial mass distribution (resulting in the IDP tilt), but ELOs are still a two-parameter family where the two parameters are correlated. The physical origin of these trends presumably lies in the systematic decrease, with increasing ELO mass, of the relative amount of dissipation experienced by the baryonic mass component along ELO stellar mass assembly. ELOs also show kinematical segregation, but it does not appreciably change with the mass scale. The non-homogeneous population of IDPs explains the role played by the virial mass to determine the correlations among intrinsic parameters. In this paper we also show that the central stellar line-of-sight velocity dispersion of ELOs, is a fair empirical estimator of the virial mass, and this explains the central role played by this quantity at determining the observational correlations.