Absence of self-averaging and of homogeneity in the large scale galaxy distribution

TL;DR

This paper reveals that galaxy distributions exhibit large-scale inhomogeneities and lack self-averaging properties beyond 30 Mpc/h, challenging standard cosmological models and suggesting a fractal-like structure at large scales.

Contribution

It introduces a new analysis method to map galaxy structures and tests the assumption of self-averaging, providing evidence against homogeneity at large scales in SDSS data.

Findings

Galaxy structures show large amplitude density fluctuations at all scales.

Two-point correlations are self-averaging up to ~30 Mpc/h with a fractal dimension D=2.1.

Density fluctuations remain large and extended beyond 30 Mpc/h, incompatible with standard models.

Abstract

The properties of the galaxy distribution at large scales are usually studied using statistics which are assumed to be self-averaging inside a given sample. We present a new analysis able to quantitatively map galaxy large scale structures while testing for the stability of average statistical quantities in different sample regions. We find that the newest samples of the Sloan Digital Sky Survey provide unambiguous evidence that galaxy structures correspond to large amplitude density fluctuations at all scales limited only by sample sizes. The two-point correlations properties are self-averaging up to approximately 30 Mpc/h and are characterized by a fractal dimension D=2.1 +- 0.1. Then at all larger scales probed density fluctuations are too large in amplitude and too extended in space to be self-averaging inside the considered volumes. These inhomogeneities are compatible with a continuation of fractal correlations but incompatible with: (i) a homogeneity scale smaller than 100 Mpc/h, (ii) predictions of standard theoretical models, (iii) mock galaxy catalogs generated from cosmological Nbody simuations.