Unexpected dancing partners: Tracing the coherence between the spin and motion of dark matter halos

TL;DR

This study uses cosmological simulations to confirm large-scale coherence between galaxy spins and neighbor motions, revealing dependencies on halo mass and local density, with implications for understanding cosmic structure formation.

Contribution

It demonstrates the extent and conditions of spin-motion coherence in dark matter halos, extending previous observational findings with simulation-based analysis.

Findings

Strong coherence within 1 Mpc/h, extending to 6 Mpc/h.

Dependence of coherence strength on halo mass and local density.

Detection of coherence signals up to 15 Mpc/h from massive halos.

Abstract

A recent study conducted using CALIFA survey data (Lee et al, 2019b) has found that the orbital motions of neighbor galaxies are coherent with the spin direction of a target galaxy on scales of many Megaparsecs. We study this so called `large-scale coherence' phenomena using N-body cosmological simulations. We confirm a strong coherence signal within 1 Mpc/h of a target galaxy, reaching out to 6 Mpc/h. We divide the simulation halos into subsamples based on mass, spin, merger history and local halo number density for both target and neighbor halos. We find a clear dependency on the mass of the target halo only. Another key parameter was the local number density of both target and neighbor halos, with high density regions such as clusters and groups providing the strongest coherence signals, rather than filaments or lower density regions. However we do not find a clear dependency on halo spin or time since last major merger. The most striking result we find is that the signal can be detected up to~15Mpc/h from massive halos. These result provide valuable lessons for how observational studies could more clearly detect coherence, and we discuss the implications of our results for the origins of large-scale coherence.