### Abstract

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.

Original language | English (US) |
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Pages (from-to) | L51-L54 |

Journal | Astrophysical Journal |

Volume | 437 |

Issue number | 1 PART 2 |

DOIs | |

State | Published - Dec 10 1994 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Cosmology: theory
- Galaxies: clustering
- Galaxies: clusters of
- Large-scale structure of universe

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## Cite this

*Astrophysical Journal*,

*437*(1 PART 2), L51-L54. https://doi.org/10.1086/187680