Bright and dark matter in elliptical galaxies:: mass and velocity distributions from self-consistent hydrodynamical simulations

We have analysed the mass and velocity distributions 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. ELOs have been identified as those virtual galaxies having a prominent, dynamically relaxed stellar spheroidal component, with no extended discs and very low gas content. Our analysis shows that they are embedded in extended, massive dark matter haloes, and they also have an extended corona of hot diffuse gas. Dark matter haloes have experienced adiabatic contraction along their assembly process. The relative ELO dark- to bright-mass content and space distributions show broken homology, and they are consistent with observational results on the dark matter fraction at the central regions, as well as on the gradients of the mass-to-light ratio profiles for boxy ellipticals, as a function of their stellar masses. These results indicate that massive ellipticals miss stars (i.e. baryons) at their central regions, as compared to less massive ones. Our simulations indicate that these missing baryons could be found beyond the virial radii as a hot, diffuse plasma. This mass homology breaking could have important implications to explain the physical origin of the Fundamental Plane relation. The projected stellar mass profiles of our virtual ellipticals can be well fitted by the Sersic formula, with shape parameters n that agree, once a stellar mass-to-light ratio independent of position is assumed, with those obtained from surface brightness profiles of ellipticals. The agreement includes the empirical correlations of n with size, luminosity and velocity dispersion. The total mass density profiles show a power-law behaviour over a large r/r(vir) interval, consistent with data on massive lens ellipticals at shorter radii. The velocity dispersion profiles show kinematical segregation, with no systematic mass dependence (i.e. no dynamical homology breaking) and a positive anisotropy (i.e. radial orbits), roughly independent of the radial distance outside the central regions. The line-of-sight (LOS) velocity dispersion profiles are declining. These results give, for the first time from cosmological simulations, a rather detailed insight into the intrinsic mass and velocity distributions of the dark, stellar and gaseous components of virtual ellipticals. The consistency with observations strongly suggests that they could also describe important intrinsic characteristics of real ellipticals, as well as some of their properties recently inferred from observational data (e.g. downsizing, the appearance of blue cores, the increase of the stellar mass contributed by the elliptical population as z decreases).