Counterrotating galaxies and memory of cosmological initial conditions
N. Voglis1, M. Harsoula2 1 Department of Astronomy - University of Athens, Greece 2 Research Center of Astronomy - Academy of Athens, Greece
As it is known, a good number of elliptical galaxies are observed to have counter rotating cores.
A popular scenario to explain the formation of such galaxies is based on the assumption that they
formed by a process of merging of other galaxies, formed ea rlier. An alternative mechanism,
proposed recently (Harsoula and Voglis 1998), could also be responsible for the formation of these
galaxies directly from cosmological initial conditions. In this study the novel mechanism was
demostrated by using quiet cosmological initial conditions in N-body simulations. We extend our
N-body simulations using clumpy initial conditions and show that this mechanism still works to
create counter rotating galaxies. Counter rotation comes out as a result of the considerable
amount of memory of initial conditions surviving for times comparable to the Hubble time, inspite
the large degree of instability of individual orbits and the dramatic redistribution and mixing of
particles in phase space. We show, for example, that particles remember, in a statistical sense,
not only their distance from the center of mass (memory of energy), but also the initial
orientation of their position relative to the direction of an external tidal field which determines
the sign and the amount of angula r momentum that is transferred to particles of the system.