Statistical Properties of the Spatial Distribution of Galaxies

TL;DR

This paper investigates the fractal nature and irregularities in galaxy distributions using correlation and radial distribution methods, revealing scale-dependent applicability and estimating a fractal dimension around 2.2.

Contribution

It clarifies the valid scale range for correlation methods in fractal analysis and provides new estimates of the galaxy distribution's fractal dimension from 2dF and 6dF data.

Findings

Correlation methods are valid only at specific scale lengths.

Estimated fractal dimension of galaxy distribution is approximately 2.2.

Significant irregularities are observed up to 70 Mpc scale.

Abstract

The methods of determining the fractal dimension and irregularity scale in simulated galaxy catalogs and the application of these methods to the data of the 2dF and 6dF catalogs are analyzed. Correlation methods are shown to be correctly applicable to fractal structures only at the scale lengths from several average distances between the galaxies, and up to (10-20)% of the radius of the largest sphere that fits completely inside the sample domain. Earlier the correlation methods were believed to be applicable up to the entire radius of the sphere and the researchers did not take the above restriction into account while finding the scale length corresponding to the transition to a uniform distribution. When an empirical formula is applied for approximating the radial distributions in the samples confined by the limiting apparent magnitude, the deviation of the true radial distribution from the approximating formula (but not the parameters of the best approximation) correlate with fractal dimension. An analysis of the 2dF catalog yields a fractal dimension of 2.20 +-m 0.25 on scale lengths from 2 to 20 Mpc, whereas no conclusive estimates can be derived by applying the conditional density method for larger scales due to the inherent biases of the method. An analysis of the radial distributions of galaxies in the 2dF and 6dF catalogs revealed significant irregularities on scale lengths of up to 70 Mpc. The magnitudes and sizes of these irregularities are consistent with the fractal dimension estimate of D = 2.1-2.4