Evolution of Structure in Cold Dark Matter Universes
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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 both a
flat and an open model with Omega_0=0.3, and two models with Omega=1, one with
the standard CDM power spectrum and the other with the same power spectrum as
the Omega_0=0.3 models. The amplitude of primordial fluctuations is set so that
the models reproduce the observed abundance of rich galaxy clusters by the
present day. The mass 2-point correlation function and power spectrum of all
the simulations 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 Omega=1 models the required bias is always greater than unity, but in
the Omega_0=0.3 models an "antibias" is required on scales smaller than \sim
5\hmpc. 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, 1-particle or
pairwise velocity dispersions. This similarity is a direct consequence of our
adopted normalisation. 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.
