The small-scale velocity dispersion of galaxies: A comparison of cosmological simulations

Rachel S. Somerville, Joel Primack, Richard Nolthenius

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The velocity dispersion of galaxies on small scales (r ∼ 1 h-1 Mpc), σ12(r), can be estimated from the anisotropy of the galaxy-galaxy correlation function in redshift space (Davis & Peebles). We apply this technique to "mock catalogs" extracted from N-body simulations of several different variants of cold dark matter-dominated cosmological models, including models with cold + hot dark matter, to obtain results that may be compared consistently with similar results from observations. We find a large variation in the value of σ12(1 h-1 Mpc) in different regions of the same simulation. We investigate the effects of removing clusters from the simulations, using an automated cluster-removing routine, and find that this reduces the sky variance but also reduces the discrimination between models. However, studying σ12 as clusters with different internal velocity dispersions are removed leads to interesting information about the amount of power on cluster and subcluster scales. We compute the pairwise velocity dispersion directly, in order to check the Davis-Peebles method, and find agreement of better than 20% in all the models studied. We also calculate the mean streaming velocity and the pairwise peculiar velocity distribution in the simulations, and compare these with the models used in the Davis-Peebles method. We find that the model for the mean streaming velocity may be a substantial source of error in the calculation of σ12.

Original languageEnglish (US)
Pages (from-to)606-615
Number of pages10
JournalAstrophysical Journal
Issue number2 PART I
StatePublished - 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Cosmology: theory
  • Galaxies: clusters: general
  • Galaxies: distances and redshifts
  • Large-scale structure of universe


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