SIMBAD references

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<sub>vir</sub>≃2 Mpc (with H<sub>0</sub>=50 km.s<sup>–1</sup>.Mpc<sup>–1</sup>), and is simulated using a force resolution of 1.0 kpc (≡0.05% of R<sub>vir</sub>); the final virial mass is 4.3x10<sup>14</sup> M<sub>☉</sub>, equivalent to a circular velocity of v<sub>circ</sub>≡(GM/R)<sup>1/2</sup>≃1000 km.s<sup>–1</sup> 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>10¹¹ 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_v3D,halos/σ_v3D,DM≃1.2-1.3); however, this effect appears to depend on numerical resolution.