COUNTERROTATING GALAXIES FORMED BY COSMOLOGICAL COLLAPSES

We investigate numerically the possibility that dissipationless cosmol ogical collapses can lead to the formation of counterrotating galaxies . We consider systems formed from initially small density excesses emb edded in the environment of other density perturbations in an otherwis e homogeneous and isotropic expanding early Universe. We find that a c entral bar-like density excess, that can make bound a mass of the orde r of galactic mass can work as a seed able to initiate counterrotating galaxies. Such objects are formed rather naturally as a result of the partial mixing between the material in which positive angular momentu m dominates with the material in which negative angular momentum domin ates. The initial axial ratio of the bar-like perturbation is a contro l parameter in this process. Counterrotation is favored for an axial r atio approximate to 0.5. The rotational velocity profile in the relaxe d state of these configurations matches to a great extent the curves g iven from observations, for some elliptical galaxies, presenting kinem atically decoupled cores. Performing parallel simulations of the same system by N-body and by conservative technique codes we show that the rotational velocity curve, established after the relaxation, maintains its basic features even for a Hubble time. Therefore counterrotating galaxies observed today could have been formed directly from cosmologi cal initial conditions.