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Probing the large scale velocity field with clusters of galaxies

Apr, 1994
14 pages
Published in:
  • Astrophys.J.Lett. 430 (1994) L13-L16
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Abstract: (arXiv)
What is the role of clusters of galaxies in probing the large-scale velocity field of the universe? We investigate the distribution of peculiar velocities of clusters of galaxies in the popular low-density (Ω=0.3\Omega=0.3) flat Cold-Dark-Matter (CDM) cosmological model, which best fits many large-scale structure observations. An Ω=1\Omega=1 CDM model is also studied for comparison. We find that clusters of galaxies are efficient tracers of the large-scale velocity field. The clusters exhibit a Maxwellian distribution of peculiar velocities, as expected from Gaussian initial density fluctuations. The cluster 3-D velocity distribution for the Ω=0.3\Omega=0.3 model peaks at v∼400v \sim 400 km s −1~{-1}, and extends to high velocities of v∼1200v \sim 1200 km s −1~{-1}. The rms peculiar velocity of the clusters is 440440 km s −1~{-1}. Approximately 10\% of all model clusters move with high peculiar velocities of v≥700v \ge 700 km s −1~{-1}. The observed velocity distribution of clusters of galaxies is compared with the predictions from cosmological models. The observed data exhibit a larger velocity tail than seen in the model simulations; however, due to the large observational uncertainties, the data are consistent at a ∼3σ\sim 3\sigma level with the model predictions, and with a Gaussian initial density field. The large peculiar velocities reported for some clusters of galaxies (v≥3000v \geq 3000 km s −1~{-1}) are likely to be overestimated, if the current model is viable.
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