Dissipationless collapse, weak homology and central cores of elliptical galaxies

Abstract

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 R1/m law with 3-6 ≲ m ≲ 8. The stellar end-products of collapses in a dark matter halo are still well described by the R1/m law, but with 1.9 ≲ m ≲ 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 A1/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 preexisting dark matter haloes may thus have a role in determining the observed weak homology of elliptical galaxies. © 2006 RAS.