Large-scale fluctuations in the distribution of galaxies from the Two
  Degree Field Galaxy Redshift Survey
  We study statistical properties of galaxy structures in several samples
extracted from the 2dF Galaxy Redshift Survey. In particular, we measured
conditional fluctuations by means of the scale-length method and determined
their probability distribution. In this way we find that galaxy distribution in
these samples is characterized by large amplitude fluctuations with a large
spatial extension, whose size is only limited by the sample's boundaries. These
fluctuations are quite typical and persistent in the sample's volumes, and they
are detected in two independent regions in the northern and southern galactic
caps. We discuss the relation of the scale-length method to several statistical
quantities, such as counts of galaxies as a function of redshift and apparent
magnitude. We confirm previous results, which have determined by magnitude and
redshift counts that there are fluctuations of about 30% between the southern
and the northern galactic caps and we relate explicitly these counts to
structures in redshift space. We show that the estimation of fluctuation
amplitude normalized to the sample density is biased by systematic effects,
which we discuss in detail. We consider the type of fluctuations predicted by
standard cosmological models of structure formation in the linear regime and,
to study nonlinear clustering, we analyze several samples of mock-galaxy
catalogs generated from the distribution of dark matter in cosmological N-body
simulations. In this way we conclude that the galaxy fluctuations present in
these samples are too large in amplitude and too extended in space to be
compatible with the predictions of the standard models of structure formation.
