216 research outputs found
The GENGA Code: Gravitational Encounters in N-body simulations with GPU Acceleration
We describe an open source GPU implementation of a hybrid symplectic N-body
integrator, GENGA (Gravitational ENcounters with Gpu Acceleration), designed to
integrate planet and planetesimal dynamics in the late stage of planet
formation and stability analyses of planetary systems. GENGA uses a hybrid
symplectic integrator to handle close encounters with very good energy
conservation, which is essential in long-term planetary system integration. We
extended the second order hybrid integration scheme to higher orders. The GENGA
code supports three simulation modes: Integration of up to 2048 massive bodies,
integration with up to a million test particles, or parallel integration of a
large number of individual planetary systems. We compare the results of GENGA
to Mercury and pkdgrav2 in respect of energy conservation and performance, and
find that the energy conservation of GENGA is comparable to Mercury and around
two orders of magnitude better than pkdgrav2. GENGA runs up to 30 times faster
than Mercury and up to eight times faster than pkdgrav2. GENGA is written in
CUDA C and runs on all NVIDIA GPUs with compute capability of at least 2.0.Comment: Accepted by ApJ. 18 pages, 17 figures, 4 table
On the age-radius relation and orbital history of cluster galaxies
We explore the region of influence of a galaxy cluster using numerical
simulations of cold dark matter halos. Many of the observed galaxies in a
cluster are expected to be infalling for the first time. Half of the halos at
distances of one to two virial radii today have previously orbited through the
cluster, most of them have even passed through the dense inner regions of the
cluster. Some halos at distances of up to three times the virial radius have
also passed through the cluster core. We do not find a significant correlation
of ``infall age'' versus present day position for substructures and the scatter
at a given position is very large. This relation may be much more significant
if we could resolve the physically overmerged galaxies in the central region.Comment: To appear in the proceedings of IAU Colloquium 195: "Outskirts of
galaxy clusters: intense life in the suburbs", Torino, Italy, March 12-16,
200
A universal density slope - velocity anisotropy relation
One can solve the Jeans equation analytically for equilibrated dark matter
structures, once given two pieces of input from numerical simulations. These
inputs are 1) a connection between phase-space density and radius, and 2) a
connection between velocity anisotropy and density slope, the \alpha-\beta
relation. The first (phase-space density v.s. radius) has been analysed through
several different simulations, however the second (\alpha-\beta relation) has
not been quantified yet. We perform a large set of numerical experiments in
order to quantify the slope and zero-point of the \alpha-\beta relation. When
combined with the assumption of phase-space being a power-law in radius this
allows us to conclude that equilibrated dark matter structures indeed have zero
central velocity anisotropy, central density slope of \alpha_0 = -0.8, and
outer anisotropy of approximately \beta_\infinity = 0.5.Comment: 4 pages, 1 figure, to appear in the XXIst IAP Colloquium "Mass
Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005, France,
(Eds.) G. Mamon, F. Combes, C. Deffayet, B. Fort, EAS Publications Serie
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