1,438 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
A universal velocity distribution of relaxed collisionless structures
Several general trends have been identified for equilibrated,
self-gravitating collisionless systems, such as density or anisotropy profiles.
These are integrated quantities which naturally depend on the underlying
velocity distribution function (VDF) of the system. We study this VDF through a
set of numerical simulations, which allow us to extract both the radial and the
tangential VDF. We find that the shape of the VDF is universal, in the sense
that it depends only on two things namely the dispersion (radial or tangential)
and the local slope of the density. Both the radial and the tangential VDF's
are universal for a collection of simulations, including controlled collisions
with very different initial conditions, radial infall simulation, and
structures formed in cosmological simulations.Comment: 13 pages, 6 figures; oversimplified analysis corrected; changed
abstract and conclusions; significantly extended discussio
Cold Dark Matter Substructures in Early-Type Galaxy Halos
We present initial results from the "Ponos" zoom-in numerical simulations of
dark matter substructures in massive ellipticals. Two very highly resolved dark
matter halos with and and different ("violent" vs. "quiescent")
assembly histories have been simulated down to in a CDM
cosmology with a total of 921,651,914 and 408,377,544 particles, respectively.
Within the virial radius, the total mass fraction in self-bound subhalos at the present epoch is 15% for the violent
host and 16.5% for the quiescent one. At , these fractions increase to
19 and 33%, respectively, as more recently accreted satellites are less prone
to tidal destruction. In projection, the average fraction of surface mass
density in substructure at a distance of ( kpc)
from the two halo centers ranges from 0.6% to %, significantly
higher than measured in simulations of Milky Way-sized halos. The contribution
of subhalos with to the projected mass
fraction is between one fifth and one third of the total, with the smallest
share found in the quiescent host. We assess the impact of baryonic effects via
twin, lower-resolution hydrodynamical simulations that include
metallicity-dependent gas cooling, star formation, and a
delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction
produces a super-isothermal total density profile and increases the number of
massive subhalos in the inner regions of the main host. The host density
profiles and projected subhalo mass fractions appear to be broadly consistent
with observations of gravitational lenses.Comment: 14 pages, 15 figures, accepted for publication in ApJ after minor
revisions, note the new Fig.
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