The Radial Orbit Instability in Collisionless N-Body Simulations

Abstract

Using a suite of self-gravitating, collisionless N-body models, we systematically explore a parameter space relevant to the onset and behavior of the radial orbit instability (ROI), whose strength is measured by the systemic axis ratios of the models. We show that a combination of two initial conditions, namely the velocity anisotropy and the virial ratio, determines whether a system will undergo ROI and exactly how triaxial the system will become. A third initial condition, the radial shape of the density profile, plays a smaller, but noticeable role. Regarding the dynamical development of the ROI, the instability a) begins after systems collapse to their most compact configuration and b) evolves fastest when a majority of the particles have radially anisotropic orbits while there is a lack of centrally-concentrated isotropic orbits. We argue that this is further evidence that self-reinforcing torques are the key to the onset of the ROI. Our findings support the idea that a separate orbit instability plays a role in halting the ROI.

accepted for publication in ApJ. 9 figures in emulateapj style

References in corpus (5)

• On Universal Halos and the Radial Orbit Instability
• The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure
• Orbital Instabilities in a Triaxial Cusp Potential
• On the equilibrium morphology of systems drawn from spherical collapse experiments
• Density Profiles of Collisionless Equilibria. II. Anisotropic Spherical Systems

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