Adaptive Refinement Tree: A New HighResolution NBody Code for Cosmological Simulations
Abstract
We present a new highresolution Nbody algorithm for cosmological simulations. The algorithm employs a traditional particlemesh technique on a cubic grid and successive multilevel relaxations on the finer meshes, introduced recursively in a fully adaptive manner in the regions where the density exceeds a predefined threshold. The mesh is generated to effectively match an arbitrary geometry of the underlying density fielda property particularly important for cosmological simulations. In a simulation the mesh structure is not created at every time step but is properly adjusted to the evolving particle distribution. The algorithm is fast and effectively parallel: the gravitational relaxation solver is approximately half as fast as the fast Fourier transform solver on the same number of mesh cells. The required CPU time scales with the number of cells, N_{c}, as ~O(N_{c}). The code allows us to improve considerably the spatial resolution of the particlemesh code without loss in mass resolution. We present a detailed description of the methodology, implementation, and tests of the code.
We further use the code to study the structure of dark matter halos in highresolution (~2 h^{1} kpc) simulations of standard CDM (Ω = 1, h = 0.5, σ_{8} = 0.63) and ΛCDM (Ω_{Λ} = 1  Ω_{0} = 0.7, h = 0.7, σ_{8} = 1.0) models. We find that halo density profiles in both CDM and ΛCDM models are well fitted by the analytical model presented recently by Navarro et al., which predicts a singular [ρ(r) ~ r^{1}] behavior of the halo density profiles at small radii. We therefore conclude that halos formed in the ΛCDM model have structure similar to that of CDM halos and thus cannot explain the dynamics of the central parts of dwarf spiral galaxies, as inferred from the galaxies' rotation curves.
 Publication:

The Astrophysical Journal Supplement Series
 Pub Date:
 July 1997
 DOI:
 10.1086/313015
 arXiv:
 arXiv:astroph/9701195
 Bibcode:
 1997ApJS..111...73K
 Keywords:

 METHODS: NUMERICAL;
 COSMOLOGY: THEORY;
 COSMOLOGY: DARK MATTER;
 Methods: Numerical;
 Cosmology: Theory;
 Cosmology: Dark Matter;
 Astrophysics;
 Physics  Computational Physics
 EPrint:
 revised in accord with published version, LaTeX (uses aaspp4.sty), 42 pages, 12 figures, all PostScript figures are available at http://astro.nmsu.edu/~akravtso/GROUP/group_publications.html or at ftp://charon.nmsu.edu/pub/kravtsov/PAPERS/ART