Testing isotropy in the Universe using photometric and spectroscopic
  data from the SDSS
  We analyze two volume limited galaxy samples from the SDSS photometric and
spectroscopic data to test the isotropy in the local Universe. We use
information entropy to quantify the global anisotropy in the galaxy
distribution at different length scales and find that the galaxy distribution
is highly anisotropic on small scales. The observed anisotropy diminishes with
increasing length scales and nearly plateaus out beyond a length scale of 200
Mpc/h in both the datasets. We compare these anisotropies with those predicted
by the mock catalogues from the N-body simulations of the Lambda CDM model and
find a fairly good agreement with the observations. We find a small residual
anisotropy on large scales which decays in a way that is consistent with the
linear perturbation theory. The slopes of the observed anisotropy converge to
the slopes predicted by the linear theory beyond a length scale of ~ 200 Mpc/h
indicating a transition to isotropy. We separately compare the anisotropies
observed across the different parts of the sky and find no evidence for a
preferred direction in the galaxy distribution.
