Large-Scale Structure of the Universe and Cosmological ...

Fig. 45. The Sp parameters for p = 3,4,5 (from bottom to top) for dark matter
(solid) and galaxies (dot-dashed) as a function of smoothing scale R. These
predictions correspond to those of the halo model, for galaxies they assume that
〈 Ngal 〉 = (m/m0) 0.8 for m > m0 = 8 × 10 11 M⊙h −1 , 〈Ngal 〉 = (m/m0) for
mc < m < m0 and 〈 Ngal 〉 = 0 for m < mc = 4 × 10 9 M⊙h −1 .
The weighing introduced by the 〈 N n gal(m) 〉 on clustering statistics has many
desirable properties. In particular, the suppression of galaxy formation in highmass
halos leads to a galaxy power spectrum that displays power-law-like behavior
91 [36,579,495,570] and higher-order correlations show smaller amplitudes
at small scales than their dark matter counterparts [570] (see Fig. 45),
as observed in galaxy catalogs. A very important additional consideration is
that this high-mass suppression also leads to velocity dispersion of galaxies in
agreement with galaxy surveys such as LCRS [349].
7.2 Projection Effects
This subsection is devoted to the particular case of angular surveys. These
surveys constitute a large part of the available data and allow to probe the
statistical properties of the cosmic density field at large scales, as we shall
discuss in the next chapter, and furthermore they do not suffer from redshiftspace
distortions. Although they do not really probe new aspects of gravitational
dynamics, the filtering scheme deserves a specific treatment. It is also
worth noting here, as we shall briefly discuss in the next section, that this
filtering directly applies to weak lensing observations that are now emerging,
see e.g. [453] for a review.
91 In addition, note that a power-law behavior has also been obtained in numerical
simulations by selecting ‘galaxies’ as halos of specific circular velocities [141].
194