Dissipationless collapse, weak homology and central cores of elliptical galaxies

By means of high-resolution N-body simulations, we revisited the dissipationless collapse scenario for galaxy formation. We considered both single-component collapses and collapses of a cold stellar distribution in a live dark matter halo. Single-component collapses lead to stellar systems whose projected profiles are fitted very well by the Sersic R-1/m law with 3.6 less than or similar to m less than or similar to 8. The stellar end-products of collapses in a dark matter halo are still well described by the R-1/m law, but with 1.9 less than or similar to m less than or similar to 12, where the lowest m values are obtained when the halo is dominant. In all the explored cases, the profiles at small radii deviate from their global best-fitting R-1/m model, being significantly flatter. The break-radius values are comparable with those measured in 'core' elliptical galaxies, and are directly related to the coldness of the initial conditions. The dissipationless collapse of initially cold stellar distributions in pre-existing dark matter haloes may thus have a role in determining the observed weak homology of elliptical galaxies.