A neighbor Search Code for Galaxies - Preliminary Results
  We present preliminary results of applying a neighbour search code to a large
sample of galaxies drawn from the Sloan Digitial Sky Survey (SDSS). We draw our
sample of target galaxies from the spectroscopic catalogue of the SDSS, which
has redshift measurements for all its $\sim8\times10^5$ galaxies. We count the
neighbours from the photometric catalogue of the SDSS, which is a flux-limited
catalogue that has a photometric redshift estimation for all its
$\sim2\times10^8$ galaxies. The code counts the number (N) of galaxies within a
given 3D-distance from the target galaxy, using a database manager and a simple
decision tree. The 3D-distance is composed of a 2D projected distance on the
sky and a radial component, which is the difference between the spectroscopic
target redshift and the photometric redshift of the "neighbour" galaxies. As we
keep the search volume constant throughout the sample, N is a proxy for the
number density of galaxies around the target galaxies. We also present an
analysis of the preliminary results, showing the relation between N, the
inferred morphology and the dominant activity type of the target galaxies, as
well as the relation between N and the star formation history of the target
galaxies.
