Breaking of self-averaging properties and selection effects in the Luminous Red Galaxies sample

Abstract

We study the statistical properties of the Luminous Red Galaxies sample from the Sloan Digital Sky Survey. In particular we test, by determining the probability density function (PDF) of galaxy (conditional) counts in spheres, whether statistical properties are self-averaging within the sample. We find that there are systematic differences in the shape of the PDF and in the location of its peak, signaling that there are major systematic effects in the data which make the estimation of volume average quantities unreliable within this sample. We discuss that these systematic effects are related to the fluctuating behavior of the redshift counts which can be originated by intrinsic fluctuations in the galaxy density field or by observational selection effects. The latter possibility implies that more than 20 % of the galaxies have not been observed and that such a selection should not be a smooth function of redshift.