1999/10/31 by Sebastiano Ghigna, Ben Moore, Fabio Governato +4 · 537 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Cluster (spacecraft) #Cold dark matter #Concentration parameter #Dark matter #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Halo #Physics #Quantum mechanics #RADIUS #Resolution (logic) #Stellar, planetary, and galactic studies #Substructure #Virial theorem #astro-ph
paper · pdf · doi:10.1086/317221
published in The Astrophysical Journal 544(2), 616-628 (IOP Publishing) · 19 pages, 13 figures, ApJ, in press. Text significantly clarified
arxiv created 2000/09/29 · openalex publication_date 2000/12/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/08
Can dissipationless N -body simulations be used to reliably determine the structural and substructure properties of dark matter halos? A large simulation of a galaxy cluster in a cold dark matter universe is used to increase the force and mass resolution of current "high-resolution simulations" by almost an order of magnitude to examine the convergence of the important physical quantities. The cluster contains ~5 million particles within the final virial radius, R vir ≃ 2 Mpc (with H 0 = 50 km s -1 Mpc -1 ), and is simulated using a force resolution of 1.0 kpc (≡0.05% of R vir ); the final virial mass is 4.3 × 10 14 M ☉ , equivalent to a circular velocity of v circ ≡ ( GM / R ) 1/2 ≃ 1000 km s -1 at the virial radius. The central density profile has a logarithmic slope of -1.5, identical to lower resolution studies of the same halo, indicating that the profiles measured from simulations of this resolution have converged to the "physical" limit down to scales of a few kpc (~0.2% of R vir ). In addition, the abundance and properties of substructure are consistent with those derived from lower resolution runs; from small to large galaxy scales ( v circ > 100 km s -1 , m > 10 11 M ☉ ), the circular velocity function and the mass function of substructures can be approximated by power laws with slopes of ~-4 and ~-2, respectively. At the current resolution, overmerging (a numerical effect that leads to structureless virialized halos in low-resolution N -body simulations) seems to be globally unimportant for substructure halos with circular velocities of v circ > 100 km s -1 (~10% of the cluster's v circ ). We can identify subhalos orbiting in the very central region of the cluster ( R ≲ 100 kpc), and we can trace most of the cluster progenitors from high redshift to the present. The object at the cluster center (the dark matter analog of a cD galaxy) is assembled between z = 3 and z = 1 from the merging of a dozen halos with v circ ≳ 300 km s -1 . Tidal stripping and halo-halo collisions decrease the mean circular velocity of the substructure halos by ≈20% over a 5 billion yr period. We use the sample of 2000 substructure halos to explore the possibility of biases using galactic tracers in clusters: the velocity dispersions of the halos globally agree with the dark matter within ≲10%, but the halos are spatially antibiased, and in the very central region of the cluster ( R / R vir < 0.3) they show positive velocity bias ( b v ≡ σ v 3D,halos /σ v 3D,DM ≃ 1.2-1.3); however, this effect appears to depend on numerical resolution.