Galaxy-group (halo) alignments from SDSS DR7 and the ELUCID simulation

TL;DR

This study investigates the alignment of galaxies with their host groups and subhalos using SDSS data and the ELUCID simulation, revealing color and mass dependence in the alignment signals.

Contribution

It introduces a novel neighborhood abundance matching method to connect observed galaxies with simulated subhalos, enhancing understanding of galaxy-halo alignments.

Findings

Red central galaxies show stronger alignment than blue centrals.

Galaxy and subhalo major axes are aligned, especially in more massive halos.

Simulation alignments are slightly stronger than observational ones.

Abstract

Based on galaxies from the Sloan Digital Sky Survey (SDSS) and subhalos in the corresponding reconstructed region from the constrained simulation of ELUCID, we study the alignment of central galaxies relative to their host groups in the group catalog, as well as the alignment relative to the corresponding subhalos in the ELUCID simulation. Galaxies in observation are matched to dark matter subhalos in the ELUCID simulation using a novel neighborhood abundance matching method. In observation, the major axes of galaxies are found to be preferentially aligned to the major axes of their host groups. There is a color dependence of galaxy-group alignment that red centrals have a stronger alignment along the major axes of their host groups than blue centrals. Combining galaxies in observation and subhalos in the ELUCID simulation, we also find that central galaxies have their major axes to be aligned to the major axes of their corresponding subhalos in the ELUCID simulation. We find that the galaxy-group and galaxy-subhalo alignment signals are stronger for galaxies in more massive halos. We find that the alignments between main subhalos and the SDSS matched subhalo systems in simulation are slightly stronger than the galaxy-group alignments in observation.