Evolution of central galaxy alignments in simulations

Abstract

Context. Observations suggest that red central galaxies align closely with their group galaxies and the large-scale environment. This finding was also replicated in simulations, which added information about the alignment of the stars that form the galaxies with the dark matter in the halo they inhabit. These results were obtained for the present Universe. Our study aims to build upon previous findings by examining the evolution of central galaxy alignment with the environment, as well as the alignment between the stellar and dark matter components. Aims. Based on previous studies, in this work, we describe the evolution of the alignment of bright central galaxies over time and try to understand the process leading to the current observed alignment. Methods. By employing the merger trees from the simulation, we tracked the alignment evolution of the central galaxy sample at z = 0 used in a previous study, the results of which correspond to observations. In particular, we exploited the anisotropic correlation function to study the alignment of the central galaxies with their environment and the probability distribution of the angle between the axes of the shape tensor calculated for each component to deepen the analysis of the stellar and dark matter components. Results. We provide a description of the evolution of alignment in bright central galaxies with a focus on the distinctions between red and blue galaxies. Furthermore, we find that the alignment of the dark matter halo differs from that of the stellar material within it. According to these findings, the assembly process and mergers influenced the evolution of the alignment.