Anisotropy of satellite galaxies. I. Contrasting correlations with central galaxy, host halo, and large-scale filament structures

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 M200c ≈ 1011 M⊙. We identify a clear 3σ scale-dependent transition in the structural tracers of satellite anisotropy: satellite distributions correlate with central galaxy morphology at small scales (<0.3R200c), are governed by host halo triaxiality at halo scales (0.3–2R200c), and align with cosmic filaments beyond 2R200c. 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 (<2R200c), explaining the shift in dominant structural tracers across scales.