COHERENT STRUCTURES IN THE UNIVERSE AND THE ADHESION MODEL

We use the adhesion model to study the formation process of large-scale structures due to nonlinear gravitational growth of small initial fluctuations in the universe dominated by dark matter. First, we test the adhesion model against two-dimensional (512 x 512) N-body simulations with initial power-law spectral indices n = -2, 0, +2, and various cutoffs. We find that the adhesion model imitates the skeleton of the structure extremely well for all choices for the parameters of the initial spectra until the stage when the nonlinear scale reaches the correlation length R(phi) of the initial gravitational potential. The adhesion model naturally explains the origin of large-scale coherent structures such as superpancakes and superfilaments, as a result of coherent motion of clumps due to large-scale inhomogeneities in the initial gravitational potential. This can happen in all kinds of initial conditions, not just traditional " pancake " models. Coherent structures can form up to size approximately R(phi) and beyond R(phi) nonlinear evolution does not produce extended coherent objects. We find that clumps of mass identified in the N-body simulations correspond to several knots in the adhesion model, which influences the way of calculating the mass distribution function. We also find that the distribution functions of velocities and masses of clumps and areas of cells in the adhesion model satisfy self-similar scaling laws of the n = 2 model.