Investigating the Binggeli Effect: The Alignment and Orientation of Brightest Cluster Galaxies with Redshift using HSC data

Abstract

In this thesis, we examine the alignment between Brightest Cluster Galaxies (BCGs) and the orientation of their clusters. In particular, we are aiming to determine whether their alignment is dependent on redshift, which other studies (discussed in the introduction) have suggested. To do this, we use the Hyper Suprime-Cam (HSC) s18a v2 catalogue to analyse 13373 clusters at 0.1 < z < 1.2. We then calculate the axial ratio and the orientation angle for both the BCGs and their host clusters. The initial results using these 13373 clusters show no correlation between alignment and redshift. We then impose certain criteria, selecting clusters with a large enough cluster size and a low enough redshift due to uncertainty in those objects (N > 30, z < 0.8), as well as the imposition that the BCG must have an axial ratio far enough from unity so that it has a well-defined orientation (\(\alpha\) < 0.8). Doing so still reveals no evidence for alignment at all, and certainly no evidence for redshift dependence. We additionally find no correlation between dominance and alignment. Further work is recommended to assess if there are any statistical or technical problems that may be affecting these results, as well as a more thorough review of the prior evidence suggesting that there is a redshift dependence.