We present results of a study on the evolution of the parameters
characterizing the structure and dynamics of the relaxed elliptical-like
objects (ELOs) identified at z=0, z=1 and z=1.5 in a set of hydrodynamical,
self-consistent simulations operating in the context of a concordance
cosmological model. The values of the stellar mass, the stellar half-mass
radius and the stellar mean-square velocity have been measured in each ELO and
found to populate, at any z, a flattened ellipsoid close to a plane (the
dynamical plane, DP). Our simulations indicate that, at the intermediate zs
considered, individual ELOs evolve, increasing the values of these parameters
as a consequence of on-going mass assembly, but, nevertheless, their DP is
roughly preserved within its scatter, in agreement with observations of the
Fundamental Plane of ellipticals at different zs. We briefly discuss how this
lack of significant dynamical and structural evolution in ELO samples arises,
in terms of the two different phases operating in the mass aggregation history
of their dark matter halos. According with our simulations, most dissipation
involved in ELO formation takes place at the early violent phase, causing the
stellar mass, the stellar half-mass radius and the stellar mean-square velocity
parameters to settle down to the DP, and, moreover, the transformation of most
of the available gas into stars. In the subsequent slow phase, ELO stellar mass
growth preferentially occurs through non-dissipative processes, so that the DP
is preserved and the ELO star formation rate considerably decreases. These
results hint, for the first time, to a possible way of explaining, in the
context of cosmological simulations, different apparently paradoxical
observational results on ellipticals.Comment: 12 pages, 1 figure. Minor changes to match the published versio