73 research outputs found
Global enhancement and structure formation of the magnetic field in spiral galaxies
We study numerically large-scale magnetic field evolution and its enhancement
in gaseous disks of spiral galaxies. We consider a set of models with the
various spiral pattern parameters and the initial magnetic field strength with
taking into account gas self-gravity and cooling/heating. In agreement with
previous studies, we find out that galactic magnetic field is mostly aligned
with gaseous structures, however small-scale gaseous structures (spurs and
clumps) are more chaotic than the magnetic field structure. In spiral arms
magnetic field strongly coexists with the gas distribution, in the inter-arm
region we see filamentary magnetic field structure. Simulations reveal the
presence of the small-scale irregularities of the magnetic field as well as the
reversal of magnetic field at the outer edge of the large-scale spurs. We
provide evidences that the magnetic field in the spiral arms has a stronger
mean-field component, and there is a clear inverse correlation between gas
density and plasma-beta parameter, compared to the rest of the disk with a more
turbulent component of the field and an absence of correlation between gas
density and plasma-beta. We show the mean field growth up to 3-10 in the
cold gas during several rotation periods (500-800 Myr), whereas ratio between
azimuthal and radial field is equal to 4/1. Mean field strength increases by a
factor of 1.5-2.5 for models with various spiral pattern parameters. Random
magnetic field component can reach up to 25 % from the total strength. By
making an analysis of the time-depended evolution of radial Poynting flux we
point out that the magnetic field strength is enhanced stronger at the galactic
outskirts which is due to the radial transfer of magnetic energy by the spiral
arms pushing the magnetic field outward. Our results also support the presence
of sufficient conditions for development of MRI at distances >11 kpc.Comment: 15 pages, 15 figures, accepted for publication in A&
New features of parallel implementation of N-body problems on GPU
This paper focuses on the parallel implementation of a direct -body
method~(particle-particle algorithm) and the application of multiple GPUs for
galactic dynamics simulations. Application of a hybrid OpenMP-CUDA technology
is considered for models with a number of particles . By
means of -body simulations of gravitationally unstable stellar galactic we
have investigated the algorithms parallelization efficiency for various Nvidia
Tesla graphics processors~(K20, K40, K80). Particular attention was paid to the
parallel performance of simulations and accuracy of the numerical solution by
comparing single and double floating-point precisions~(SP and DP). We showed
that the double-precision simulations are slower by a factor of~ than the
single-precision runs performed on Nvidia Tesla K-Series processors. We also
claim that application of the single-precision operations leads to incorrect
result in the evolution of the non-axisymmetric gravitating -body systems.
In particular, it leads to significant quantitative and even qualitative
distortions in the galactic disk evolution. For instance, after
integration time steps for the single-precision numbers the total energy,
momentum, and angular momentum of a system with conserve with
accuracy of , and respectively, in comparison to
the double-precision simulations these values are , and
, respectively. Our estimations evidence in favour of usage of the
second-order accuracy schemes with double-precision numbers since it is more
efficient than in the fourth-order schemes with single-precision numbers.Comment: 12 pages, 7 figure
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