Very large scale correlations in the galaxy distribution
  We characterize galaxy correlations in the Sloan Digital Sky Survey by
measuring several moments of galaxy counts in spheres. We firstly find that the
average counts grows as a power-law function of the distance with an exponent
D= 2.1+- 0.05 for r in [0.5,20] Mpc/h and D = 2.8+-0.05 for r in [30,150]
Mpc/h. In order to estimate the systematic errors in these measurements we
consider the counts variance finding that it shows systematic finite size
effects which depend on the samples sizes. We clarify, by making specific
tests, that these are due to galaxy long-range correlations extending up to the
largest scales of the sample. The analysis of mock galaxy catalogs, generated
from cosmological N-body simulations of the standard LCDM model, shows that for
r<20 Mpc/h the counts exponent is D~2.0, weakly dependent on galaxy luminosity,
while D=3 at larger scales. In addition, contrary to the case of the observed
galaxy samples, no systematic finite size effects in the counts variance are
found at large scales, a result that agrees with the absence of large scale,
r~100 Mpc/h, correlations in the mock catalogs. We thus conclude that the
observed galaxy distribution is characterized by correlations, fluctuations and
hence structures, which are larger, both in amplitude and in spatial extension,
than those predicted by the standard model LCDM of galaxy formation.
