Triaxiality Inhibitors in N-Body Simulations

TL;DR

This paper investigates a proposed orbital instability that could prevent triaxial shapes in N-body systems, but finds that finite-N effects complicate the interpretation, raising questions about the reliability of simulations for real-world dark matter halos.

Contribution

The study verifies a previously described orbital instability and explores its presence in N-body simulations, highlighting the influence of finite-N effects on shape predictions.

Findings

The orbital instability is present in numerical orbit integrations.

Finite-N effects can mimic the instability in simulations.

Predicting real system shapes from simulations involves significant uncertainty.

Abstract

Numerous previous studies have investigated the phenomenon wherein initially spherical N-body systems are distorted to triaxial shapes. We report on an investigation of a previously described orbital instability that should oppose triaxiality. After verifying the instability with numerical orbit integrations that extend the original analysis, we search for evidence of the instability in N-body systems that become triaxial. Our results highlight the difficulty in separating dynamical process from finite-N effects. While we argue that our analysis points to the presence of the instability in simulated triaxial systems, discreteness appears to play a role in mimicking the instability. This suggests that predicting the shapes of real-world systems, such as dark matter halos around galaxies, based on such simulations involves more uncertainty than previously thought.