4 research outputs found
On the relevance of chaos for halo stars in the Solar Neighbourhood
We show that diffusion due to chaotic mixing in the Neighbourhood of the Sun
may not be as relevant as previously suggested in erasing phase space
signatures of past Galactic accretion events. For this purpose, we analyse
Solar Neighbourhood-like volumes extracted from cosmological simulations that
naturally account for chaotic orbital behaviour induced by the strongly
triaxial and cuspy shape of the resulting dark matter haloes, among other
factors. In the approximation of an analytical static triaxial model, our
results show that a large fraction of stellar halo particles in such local
volumes have chaos onset times (i.e., the timescale at which stars commonly
associated with chaotic orbits will exhibit their chaotic behaviour)
significantly larger than a Hubble time. Furthermore, particles that do present
a chaotic behaviour within a Hubble time do not exhibit significant diffusion
in phase space.Comment: 20 pages, 16 figures. Accepted for publication in MNRA
On the relevance of chaos for halo stars in the solar neighbourhood
We show that diffusion due to chaotic mixing in the neighbourhood of the Sun may not be as relevant as previously suggested in erasing phase space signatures of past Galactic accretion events. For this purpose, we analyse solar neighbourhood-like volumes extracted from cosmological simulations that naturally account for chaotic orbital behaviour induced by the strongly triaxial and cuspy shape of the resulting dark matter haloes, among other factors. In the approximation of an analytical static triaxial model, our results show that a large fraction of stellar halo particles in such local volumes have chaos onset times (i.e. the time-scale at which stars commonly associated with chaotic orbits will exhibit their chaotic behaviour) significantly larger than a Hubble time. Furthermore, particles that do present a chaotic behaviour within a Hubble time do not exhibit significant diffusion in phase space.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
Simulating cosmological substructure in the solar neighbourhood
We explore the predictive power of cosmological, hydrodynamical simulations for stellar phase-space substructure and velocity correlations with the AURIGA simulations and AURIGAIA mock Gaia catalogues. We show that at the solar circle the AURIGA simulations commonly host phase-space structures in the stellar component that have constant orbital energies and arise from accreted subhaloes. These structures can persist for a few Gyr, even after coherent streams in position space have been erased. We also explore velocity two-point correlation functions and find this diagnostic is not deterministic for particular clustering patterns in phase space. Finally, we explore these structure diagnostics with the AURIGAIA catalogues and show that current catalogues have the ability to recover some structures in phase space but careful consideration is required to separate physical structures from numerical structures arising from catalogue generation methods
Smart: A program to automatically compute accelerations and variational equations
Modern astronomical potentials modeling galaxies or stellar systems can be
rather involved, and deriving their first derivatives (accelerations) and
second derivatives (variational equations) in order to compute orbits and their
chaoticity may be a formidable task. We present here a fully automated routine,
dubbed Smart, with which the accelerations and the variational equations of an
arbitrary potential that has been written in the Fortran 77 language can be
computed. Almost any Fortran 77 statement is admitted in the potential, and the
output are standard Fortran 77 routines ready to use. We validate our algorithm
with a set of potentials including time-dependent, velocity-dependent and very
complex potentials that even involve auxiliary routines. We also describe with
some detail a realistic seven-component Galactic potential, MilkyWayHydra,
which yields very involved derivatives, thus being a good test bed for Smart.Comment: 37 pages, 5 figures. To be published in Astronomy and Computing, in
pres