336 Highlights in modern observational cosmology
Figure 11.12. Evolution of the cosmic structure (projected mass distribution)
from z = 3 to the present, as obtained with large N-body simulations by
the VIRGO Colloboration (Jenkinset al 1998). The three models are-CDM,
S(tandard)-CDM and O(pen)-CDM with, respectively, the following parameters
(m,,,h)=( 0. 3 , 0. 7 , 0. 21 , 0. 7 ),( 1 , 0 , 0. 5 , 0. 5 ),( 0. 3 , 0 , 0. 21 , 0. 7 ).is the shape
parameter of the power spectrum. Each box is 240h−^1 Mpc across.
projected mass distribution is shown in three snapshots (z= 3 , 1 ,0), for three
different cold dark matter (CDM) models. Model parameters have been chosen
to reproduce approximately the same abundance of clusters atz=0(usinga
different normalizationσ 8 ). These simulations clearly show that the growth rate
of perturbations depends mainly onmand, to a lesser extent, on.Inlow
density models, fluctuations start growing in the early universe and stop growing
at 1+z ∼−m^1 .InSCDM(m =1) large structure form much later, and
end up evolving rapidly atz<1. The effect of the cosmological constant is
to lengthen cosmic time (figure 11.1) and to ‘counteract’ the effect of gravity,
so that perturbations cease to grow at slighly later epochs (a close inspection of