The galaxy counts-in-cells distribution from the SDSS

TL;DR

This paper analyzes the distribution of galaxy counts in SDSS data, revealing cosmic variance effects and the clustering behavior of bright galaxies, consistent with gravitational models and dark matter halo theories.

Contribution

It provides the first detailed counts-in-cells analysis of SDSS galaxies, comparing observations with theoretical distributions and examining luminosity-dependent clustering.

Findings

Counts-in-cells distributions vary by up to 20% due to cosmic variance.

Distribution agrees with gravitational quasi-equilibrium and negative binomial models.

Bright galaxies are more strongly clustered, likely in close dark matter haloes.

Abstract

We determine the galaxy counts-in-cells distribution from the Sloan Digital Sky Survey (SDSS) for 3D spherical cells in redshift space as well as for 2D projected cells. We find that cosmic variance in the SDSS causes the counts-in-cells distributions in different quadrants to differ from each other by up to 20%. We also find that within this cosmic variance, the overall galaxy counts-in-cells distribution agrees with both the gravitational quasi-equilibrium distribution and the negative binomial distribution. We also find that brighter galaxies are more strongly clustered than if they were randomly selected from a larger complete sample that includes galaxies of all luminosities. The results suggest that bright galaxies could be in dark matter haloes separated by less than ~10 Mpc/h.