EDP Sciences
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Volume 419, Number 2, May IV 2004
Page(s) 425 - 437
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20034566

A&A 419, 425-437 (2004)
DOI: 10.1051/0004-6361:20034566

Numerical study of the cosmological velocity field as a function of density

A. Domínguez1, 2 and A. L. Melott3

1  Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart, Germany
2  Theoretische Physik, Ludwig-Maximilians-Universität, Theresienstr. 37, 80333 München, Germany
3  Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA

(Received 23 October 2003 / Accepted 5 February 2004 )

We report on a new study of the velocity distribution in   N-body simulations. We investigate the center-of-mass and internal kinetic energies of coarsening cells as a function of time, cell size and cell mass. By using self-similar cosmological models, we are able to derive theoretical predictions for comparison and to assess the influence of finite-size and resolution effects. The most interesting result is the discovery of a polytropic-like relationship between the average velocity dispersion (internal kinetic energy) and the mass density in an intermediate range of densities,  ${\kappa}_{\rm int}\propto \varrho^{2-\eta}$. The exponent  $\eta$ measures the deviations from the virial prediction,   $\eta_{\rm virial}=0$. For self-similar models,  $\eta$ depends only on the spectral index of the initial power spectrum. We also study CDM models and confirm a previous result that the same polytropic-like dependence exists, with a time and coarsening length dependent  $\eta$. The dependence  ${\kappa}_{\rm int}(\varrho)$ is an important input for a recently proposed theoretical model of cosmological structure formation which improves over the standard dust model (pressureless fluid) by regularizing the density singularities.

Key words: gravitation -- methods:  N-body simulations -- cosmology: large-scale structure of Universe

Offprint request: A. Domínguez, alvaro@fluids.mpi-stuttgart.mpg.de

© ESO 2004