We determine the velocity correlation function, pairwise peculiar velocity difference, and rms pairwise peculiar velocity dispersion of rich clusters of galaxies, as a function of pair separation, for three cosmological models: Ω = 1 and Ω ;= 0.3 cold dark matter (CDM), and Ω = 0.3 primeval baryonic isocurvature (PBI) models (all flat and COBE-normalized). We find that close cluster pairs, with separation r < 10 h-1 Mpc, exhibit strong attractive peculiar velocities in all models; the cluster pairwise velocities depend sensitively on the model. The mean pairwise attractive velocity of clusters on 5 h-1 Mpc scale ranges from ∼1700 km s-1 for Ω = 1 CDM to ∼1000 km s-1 for PBI to ∼700 km s-1 for Ω = 0.3 CDM. The small-scale pairwise velocities depend also on cluster mass: richer, more massive clusters exhibit stronger attractive velocities than less massive clusters. On large scales, from ∼20 to 200 h-1 Mpc, the cluster peculiar velocities are increasingly dominated by bulk and random motions; they are independent of cluster mass. The cluster velocity correlation function is negative on small scales for Ω = 1 and Ω = 0.3 CDM, indicating strong pairwise motion relative to bulk motion on small scales; PBI exhibits relatively larger bulk motions. The cluster velocity correlation function is positive on very large scales, from r ∼ 10 h-1 Mpc to r ∼ 200 h-1 Mpc, for all models. These positive correlations, which decrease monotonically with scale, indicate significant bulk motions of clusters up to ∼200 h-1 Mpc. The strong dependence of the cluster velocity functions on models, especially at small separations, makes them useful tools in constraining cosmological models when compared with observations.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Cosmology: theory
- Galaxies: clustering
- Galaxies: clusters of
- Large-scale structure of universe