Investigation of the orientation of galaxies in clusters: the importance, methods and results of research

TL;DR

This research improves methods to analyze galaxy orientations in clusters, confirming that galaxy alignments are non-random and providing insights into galaxy formation processes.

Contribution

The paper introduces an enhanced analysis method for galaxy orientations, including spatial angles, and validates its effectiveness through application to 247 galaxy clusters.

Findings

Galaxy orientations in clusters are non-random.

Confirmed galaxy alignments are independent of cluster types.

Method comparison with simulations supports the results.

Abstract

Various models of structure formation can account for various aspects of the galaxy formation process on different scales, as well as for various observational features of structures. Thus, the investigation of galaxies orientation constitute a standard test of galaxies formation scenarios since observed variations in angular momentum represent fundamental constraints for any model of galaxy formation. We have improved the method of analysis of the alignment of galaxies in clusters. Now, the method allowed analysis both position angles of galaxy major axes and two angles describing the spatial orientation of galaxies. The distributions of analyzed angles were tested for isotropy by applying different statistical tests. For sample of analyzed clusters we have computed the mean values of analyzed statistics, checking whether they are the same as expected ones in the case of random distribution of analyzed angles. The detailed discussion of this method has been performed. We have shown how to proceed in many particular cases in order to improve the statistical reasoning when analyzing the distribution of the angles in the observational data. Separately, we have compared these new results with those obtained from numerical simulations. We show the powerful of our method on the example of galaxy orientation analysis in 247 Abell rich galaxy clusters. We have found that the orientations of galaxies in analyzed clusters are not random. It means that we genuinely confirmed an existence of the alignment of galaxies in rich Abells' galaxy clusters. This result is independent from the clusters of Bautz-Morgan types.