Evolution of Structure in Cold Dark Matter Universes

Abstract

We present an analysis of the clustering evolution of dark matter in four cold dark matter (CDM) cosmologies. We use a suite of high resolution, 17-million particle, N-body simulations which sample volumes large enough to give clustering statistics with unprecedented accuracy. We investigate a flat model with Ω 0 = 0.3, an open model also with Ω 0 = 0.3, and two models with Ω = 1, one with the standard CDM power spectrum and the other with the same power spectrum as the Ω 0 = 0.3 models. In all cases, the amplitude of primordial fluctuations is set so that the models reproduce the observed abundance of rich galaxy clusters by the present day. We compute mass two-point correlation functions and power spectra over three orders of magnitude in spatial scale and find that in all our simulations they differ significantly from those of the observed galaxy distribution, in both shape and amplitude. Thus, for any of these models to provide an acceptable representation of reality, the distribution of galaxies must be biased relative to the mass in a non-trivial, scale-dependent, fashion. In the Ω = 1 models the required bias is always greater than unity, but in the Ω 0 = 0.3 models an "antibias" is required on scales smaller than ∼ 5h −1 Mpc. The mass correlation functions in the simulations are well fit by recently published analytic models. The velocity fields are remarkably similar in all the models, whether they be characterised as bulk flows, single-particle or pairwise velocity dispersions. This similarity is a direct consequence of our adopted normalisation and runs contrary to the common belief that the amplitude of the observed galaxy velocity fields can be used to constrain the value of Ω 0 . The small-scale pairwise velocity dispersion of the dark matter is somewhat larger than recent determinations from galaxy redshift surveys, but the bulk flows predicted by our models are broadly in agreement with most available data.

Observational probes of cosmic acceleration

“…By the mid-1990s, many cosmological simulation studies included both open-CDM models and Λ-CDM models, along with Ω m = 1 models incorporating tilted inflationary spectra, nonstandard radiation components, or massive neutrino components (e.g., Ostriker and Cen 1996;Cole et al 1997;Gross et al 1998;Jenkins et al 1998). Once normalized to the observed level of CMB anisotropies, the large-scale structure predictions of open and flat-Λ models differed at the tens-of-percent level, with flat models generally yielding a more natural fit to the observations (e.g., Cole et al 1997).…”

The Dark Side of the Halo Occupation Distribution

“…High-resolution cosmological simulations over the past decade have shown that on small scales (P1-2 Mpc) the correlation function of matter strongly deviates from the power-law shape. The direct implication of this result is that the spatial distribution of galaxies on small scales is biased with respect to the overall distribution of matter in a nontrivial scale-dependent way (e.g., Klypin et al 1996;Jenkins et al 1998). In view of this, it is very interesting to understand whether the power-law shape of the correlation function is a fortuitous coincidence or a consequence of some fundamental physical process.…”

XMM observation of the dynamically young galaxy cluster CL 0939+4713

“…The formation and evolution of clusters depends sensitively on cosmological parameters like the mean matter density in the universe Ω m (Thomas et al 1998;Jenkins et al 1998;Beisbart et al 2001). Therefore it is important to determine the dynamical state of clusters at different redshifts, i.e.…”