Remarks on the methods of investigations of alignment of galaxies

TL;DR

This paper reviews and improves statistical methods for analyzing galaxy alignments, demonstrating that galaxies in rich Abell clusters exhibit non-random orientations through enhanced analysis techniques.

Contribution

It introduces improved statistical tests for galaxy alignment analysis and applies them to real and simulated data, revealing non-random galaxy orientations in rich clusters.

Findings

Galaxies in rich Abell clusters show non-random orientations.

Enhanced statistical methods improve detection of galaxy alignments.

Simulations support the observed non-random alignments.

Abstract

In the 1975 Hawley and Peebles gave the proposal to use three statistical tests for investigations of the galaxies orientation in the large structures. Nowadays, it has been considered as the standard method of searching for galactic alignments. In the present paper we analyzed the tests in details and proposed a few improvements. Basing on the improvements, the new method of analysis of the alignment of galaxies in clusters is proposed. The power of this method is demonstrated on the sample of 247 Abell clusters with at least 100 objects in each. The distributions of the position angles for galaxies in each cluster are analyzed using statistical tests: $\chi^2$, Fourier, autocorrelation and Kolmogorow test. The mean value of analyzed statistics is compared with theoretical predictions as well as with results obtained from numerical simulations. We performed 1000 simulations of 247 fictious clusters, each with numbers of galaxies the same as the real ones. We found that orientations of galaxies in analyzed clusters are not random i.e. that there exists an alignment of galaxies in rich Abell galaxy clusters.