On the stability of quasi-equilibrium self-gravitating configurations in a tidal field

The possibility that quasi-equilibrium self-gravitating galaxy-like configurations exist in a tidal field is analyzed in this paper. More specifically, we address the question of how to predict initial configurations modeling galaxies that are able to survive environmental effects in a dense environment for roughly one Hubble time, provided that dynamical friction is neglected. For simplicity, the configurations in the tidal field have been taken initially to be spherically symmetric and to have an isotropic velocity dispersion tensor (t-limited King spheres); they orbit inside steady state, spherical halos, as those that presumably surround compact galaxy groups and galaxy clusters. Both circular and eccentric orbits have been considered. In both cases, the initial quasi-equilibrium configurations have been built up taking into account the external tidal field produced by the halo. It modifies the escape velocity field of the configuration, compared with isolated configurations. The survival of the configurations as they orbit inside the halos has been studied through N-body simulations. As a general result, it has been found that the bulk of the models are conserved along 12.5 Gyr of evolution and that the low rates of mass loss they experience are consistent with those expected when the adiabatic protection hypothesis is at work. So, solutions for galaxy configurations in tidal quasi-equilibrium have been found, showing that tidal stripping in quiescent phases does not seem to be very important, unless the density of the galaxy environment at its formation had been much lower than that of the galaxy environment at the point of its orbit where the tidal perturbation is maximum.