Anisotropy of Satellite Galaxies-I: Contrasting Correlations with Central Galaxy, Host Halo, and Large-Scale Filament Structures

TL;DR

This study uses cosmological simulations to analyze satellite galaxy anisotropy, revealing scale-dependent correlations with central galaxy, halo, and filament structures, driven by satellite trajectories and gravitational dynamics.

Contribution

It identifies a scale-dependent transition in satellite anisotropy origins, linking small-scale morphology to halo shape and large-scale filaments to cosmic structures.

Findings

Satellite anisotropy aligns with halo/central galaxy major axis across simulations.

A clear transition occurs at about 0.3-2 times the virial radius, shifting from galaxy morphology to filament alignment.

Satellite trajectories explain the erasure of primordial filament signals at small scales.

Abstract

Using the SIMBA, EAGLE, and IllustrisTNG-100 galaxy formation simulations, we examine the anisotropy of the satellite distribution and its dependencies on central galaxies, host halos, and cosmic filaments. We find that in all simulations the satellite anisotropy is robustly aligned with the halo/central galaxy major axis. This correlation is both redshift- and halo-mass-dependent and also extends to filamentary structures outside the halo to several virial radii. The alignment persists up to $z=1.5$ at high redshifts, and the mass dependence remains down to $M_\mathrm{200c} \approx 10^{11}M_{\odot}$. We identify a clear $3\sigma$ scale-dependent transition in the structural tracers of satellite anisotropy: satellite distributions correlate with central galaxy morphology at small scales ($<0.3R_{\rm 200c}$), are governed by host halo triaxiality at halo scales ($0.3$-$2R_{\rm 200c}$), and align with cosmic filaments beyond $2R_{\rm 200c}$. By tracing satellite trajectories in SIMBA, we uncover the kinematic origin of this transition, demonstrating that satellites prefer halo major-axis aligned regions because their trajectories intersect this axis far more frequently and stay in it for a longer time under the host's gravitational potential. This dynamical processing effectively erases primordial filament-related signals upon accretion ($<2R_{\rm 200c}$), explaining the shift in dominant structural tracers across scales.