and Cosmology

7. Cosmology II: Inhomogeneities in the Universe
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Fig. 7.10. Simulations of the dark matter distribution in the
Universe for four different cosmological models: Ω m = 0.3,
Ω Λ = 0.7 (ΛCDM), Ω m = 1.0, Ω Λ = 0.0 (SCDM and
τCDM), and Ω m = 0.3, Ω Λ = 0. (OCDM). The two Einstein–
de Sitter models differ in their shape parameter Γ which
specifies the shape of the power spectrum P(k). For each
of the models, the mass distribution is presented for three
different redshifts, z = 3, z = 1, and today, z = 0. Whereas
the current mass distribution is quite similar in all four
models (the model parameters were chosen as such), they
clearly differ at high redshift. We can see, for instance,
that significantly less structure has formed at high redshift
in the SCDM model compared to the other models. From
the analysis of the matter distribution at high redshift, one
can therefore distinguish between the different models. In
these simulations by the VIRGO Consortium, 256 3 particles
were traced; the side length of the simulated volume
is ∼ 240h −1 Mpc
to studying the statistical properties of very massive
structures, like, e.g., the distribution of galaxy clusters.
On the other hand, this large volume, together with
the limited total number of particles that can be followed,
means that the mass and spatial resolution of
this simulation are insufficient for studying galaxies.
To date (2006), by far the largest simulation is the
Millennium simulation, carried out for a cosmological
model with Ω m =0.25, Ω Λ =0.75, a power spectrum
normalization of σ 8 =0.9, and a Hubble constant of
h=0.73. A cube of side length 500h −1 Mpc was considered,
in which (2160) 3 ≈10 10 particles with a mass
of 8.6 × 10 8 h −1 M ⊙ each were traced. With this choice
of parameters, one can spatially resolve the halos of
galaxies. At the same time, the volume is large enough
for the simulation to contain a large number of massive