Alignment of the central galaxies with the environment

Abstract

In this work, we combine ellipticity and major axis position angle measurements from the Sloan Digital Sky Server Data Release 16 with the group finder algorithm of Rodriguez & Merchan to determine the alignment of the central galaxies with the surrounding structures and satellite galaxies lying in their group. We use two independent methods: a modified version of the two- point cross-correlation function and the angle between the central galaxy orientation and the satellite galaxies relative position. The first method allows us to study the inner and outer regions of the cluster, while the second method provides information within the haloes. Our results show that central galaxies present anisotropy in the correlation function up to ∼10 h -1 Mpc , which becomes ∼10 per cent stronger for the brightest ones ( 0.1 M r < -21.5). When we split the galaxy sample by colour, we find that red central galaxies are the main contributors to this anisotropy. We also show that this behaviour does not depend on the group mass or central galaxy ellipticity . Finally , our results are in agreement with previous findings, showing that the two-point cross-correlation function is a good tracer of the galaxy alignments using all galaxies and not only those of the group to which it belongs. In addition, this feature allows us to explore the behaviour of the alignment on larger scales.