The actual relevance of chaos in shaping the phase space structure of MilkyWay-like stellar halos I: Local volumes

N. P. MAFFIONE; F.A. GOMEZ; P. M. CINCOTTA; C.M. GIORDANO; B.W. O'SHEA

Buenos Aires

Workshop; Third Workshop on Numerical and Observational Astrophysics: Linking the Local Universe to the Early One; 2014

IAFE

Several studies in the past have suggested that diffusion due to chaotic mixing can be strong enough to erase signatures of accretion events otherwise present in the phase space distributions of Solar neighborhood stars. In this work, we show that this mixing mechanism may not be as significant as previously thought. Two central points regarding the possibility of chaotic mixing shaping the underlying phase space distribution are discussed. First, we estimate the magnitude of the Lyapunov time, i.e. the time?scale in which stars commonly associated with chaotic orbits will effectively reveal their chaotic behavior. Then, we revise the wide?spread assumption that chaos must inevitably lead to diffusion in phase space, i.e. large variations of the integrals of motion. For this purpose, we analyze Solar neighborhood?like volumes extracted from cosmological simulations of the formation of Milky Way dark matter halos, coupled to a semi?analytic model of galaxy formation, as provided by the Aquarius Project. These simulations naturally account for chaotic orbital behavior induced by the strongly triaxial shape of the resulting halos, among other factors. Our results show that a large fraction of stellar halo?particles located within local volumes have Lyapunov times significantly larger than a Hubble time. Furthermore, we provide examples of chaotic orbits that do not significantly exhibit large diffusion in phase space. Therefore, we suggest that chaotic mixing is not as relevant as previously thought in erasing local dynamical signatures of the formation history of Milky Way?like galaxies.