Counterrotating galaxies and memory of cosmological initial conditions

As it is known, a good number of galaxies are observed to have counterrotat ing cores. A popular scenario to explain the formation of such galaxies is based on a secondary process of merging of galaxies with their satellites, or gas infall, or merger events between galaxies. An alternative mechanism, proposed by Voglis et al., 1991, and by Harsoula and Voglis 1998, could al so be responsible for the formation of these galaxies directly from cosmolo gical initial conditions (direct scenario). The novel mechanism was demonst rated by using quiet cosmological initial conditions in N-body simulations. In the present paper we extend our N-body simulations using clumpy initial conditions and show that this mechanism still works to create counterrotat ing galaxies. Counterrotation is a result of the considerable amount of mem ory of initial conditions surviving for times comparable to the Hubble time , despite the large degree of instability of individual orbits and the dram atic redistribution and mixing of the particles in phase space. We show, fo r example, that the particles remember, in a statistical sense, not only th eir distance from the center of mass (memory of energy), but also the initi al orientation of their position relative to the direction of an external t idal field, which determines the sign and the amount of angular momentum th at is transferred to the particles of the system.