The Motions of Clusters and Groups of Galaxies

Details The Motions of Clusters and Groups of Galaxies The Motions of Clusters and Groups of Galaxies

1994-10-19

arxiv.org/abs/astro-ph/9410061v1

Astronomy and Astrophysics

Astrophysics

email: cen@astro.princeton.edu To appear in the Astrophysical Journal, November 20, 1994, compressed, uuencodedpostscript file

Scientific paper

10.1086/174877

The distributions of peculiar velocities of rich clusters and of groups of galaxies are investigated for different cosmological models and are compared with observations. Four cosmological models are studied: standard ($\Omega=1$) CDM, low-density ($\Omega=0.3$) CDM, HDM ($\Omega=1$), and PBI ($\Omega=0.3$), all COBE normalized. We find that rich clusters of galaxies exhibit a Maxwellian distribution of peculiar velocities in all models,as expected from a Gaussian initial density field. The cluster 3-D velocity distribution typically peaks at $v \sim 600$ km s$^{-1}$, and extends to high cluster velocities of $v \sim 2000$ km s$^{-1}$. The low-density CDM model exhibits somewhat lower velocities: it peaks at $\sim 400$ km s$^{-1}$, and extends to $\sim 1200$ km s$^{-1}$. Approximately 10\% ($\sim$1\% for low- density CDM) of all model rich clusters move with high peculiar velocities of $v \ge 10^3$ km s$^{-1}$. The highest velocity clusters frequently originate in dense superclusters. The model velocity distributions of groups and clusters of galaxies are compared with observations. The data exhibit a larger high-velocity tail, to $v_r \geq 2000$ km s$^{-1}$, than seen in the model simulations (except HDM). Due to the large observational uncertainties, however, the data are consistent at a $\sim 1$ to $3\sigma$ level with the model predictions and with a Gaussian initial density field. Accurate observations of cluster peculiar velocities, especially at the high-velocity tail, should provide powerful constraints on the cosmological models.

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