Galaxy Clusters and the Epoch of Galaxy Formation
Existing data sets can be used to constrain the amplitude of primordial density fluctuations and hence the epoch of galaxy formation. Velocity dispersions, x-ray temperatures and mass-to-light ratios of galaxy clusters are particularly sensitive diagnostics. The expected values of these quantities in the cold dark matter cosmogony are calculated. Comparison of the model predictions with the velocity dispersion data is hampered by projection effects inherent in the two-dimensional nature of cluster catalogues. The model predictions agree with the x-ray temperature and (M/L) data for a value of the biasing parameter b ≃ 2 − 2.5. With this normalisation the cold dark matter cosmogony predicts a recent epoch of galaxy formation with much of the activity occurring at z ≲ 2.5.
KeywordsDark Matter Velocity Dispersion Galaxy Cluster Luminosity Function Projection Effect
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