Astron. Astrophys. 329, 1-13 (1998)

2. Numerical models

In this paper the spatial distribution and evolution of the potential is investigated using six numerical simulations of the standard CDM model (SCDM) and the double inflation model leading to power spectra with broken scale invariance (BSI) (Gottlöber et al. 1991). We have chosen these two models because they base both on cold dark matter, however they possess different power spectra on the relevant scales. Nevertheless, we found quite similar results for both models. Thus we present in the following mainly figures obtained from SCDM simulations, and we provide results both from CDM and BSI in the text and in the tables. We employ particle mesh simulations with particles in cells using three computational boxes with box sizes Mpc (they are denoted by CDM200, CDM75  &  CDM25 and BSI200, BSI75  &  BSI25, respectively). A more complete description of the simulations used here is given in Kates et al. (1995). All simulations were started at redshift using the same initial random phases, where the amplitudes were calculated in accordance with the first year COBE normalisation. The power spectra for CDM and BSI models are plotted in Fig. 1.

Fig. 1. The compound power spectra for CDM & BSI models

Let us note here that due the finite resolution and finite box sizes all simulations deal with truncated power spectra. Speaking about the potential or the density in a PM-simulation, we always take the CIC values, i.e. the fields smoothed over the cell size. As measured with respect to the variance on the grid, the amplitude of initial perturbations is the largest for CDM25 and the smallest for BSI200. The simulations BSI75, BSI25, CDM200 and CDM75 are characterized by a successive growth of the initial amplitude between the extreme cases. These differences lead to a different degree of clustering at the same redshifts. For BSI200 the structure formation began not till redshift , and at the redshift we see only weakly developed structures (Doroshkevich et al. 1997a). However, in CDM25 the disruption of structures and the formation of massive clumps can already be observed at . Thus with this sample of models we can investigate the structure evolution over a wide range of evolutionary stages.

© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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