Alignment of the central galaxies with the environment

TL;DR

This study investigates how central galaxies align with their surrounding structures using SDSS data, revealing anisotropies up to 10 Mpc, especially for bright and red galaxies, independent of group mass or ellipticity.

Contribution

It introduces a combined analysis using two methods to study galaxy alignment across different scales and confirms the anisotropic distribution of central galaxies relative to their environment.

Findings

Central galaxies show anisotropy in correlation up to 10 h^{-1} Mpc.

Red central galaxies contribute most to the anisotropy.

Alignment features are independent of group mass and galaxy ellipticity.

Abstract

In this work, we combine ellipticity and major axis position angle measurements from the Sloan Digital Sky Server Data Release 16 (SDSS DR16) with the group finder algorithm of Rodriguez \& Merch\'an 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 halos. Our results show that central galaxies present anysotropy in the correlation function up to $\sim 10 h^{-1}Mpc$, which becomes $\sim$10\% stronger for the brightest ones ($^{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.