Dark halos acting as chaos controllers in asymmetric triaxial galaxy models

We study the regular or chaotic character of orbits in a 3D dynamical model, describing a triaxial galaxy surrounded by a spherical dark halo component. Our numerical experiments suggest that the percentage of chaotic orbits decreases exponentially as the mass of the dark halo increases. A linear increase of the percentage of the chaotic orbits was observed as the scale length of the halo component increases. In order to distinguish between regular and chaotic motion, we chose to use the total angular momentum Ltot of the 3D orbits as a new indicator. Comparison with other, previously used, dynamical indicators, such as the Lyapunov Characteristic Exponent or the P(f) spectral method, shows that the Ltot indicator gives very fast and reliable results for characterizing the nature of orbits in galactic dynamical models.