Cosmology using cluster internal velocity dispersions

We compare the cumulative distribution of internal velocity dispersions of galaxy clusters, N(>sigma(nu)), for a large observational sample to those obtained from a set of N-body simulations that we run for seven COBE-normalized cosmological scenarios. They are: the standard CDM (SCDM) and a tilted (n = 0.85) CDM (TCDM) model, a cold+hot DM (CHDM) model with Ohm(nu) = 0.25, two low-density flat CDM (Lambda CDM) models with Ohm(0) = 0.3 and 0.5, two open CDM (OCDM) models with Ohm(0) = 0.4 and 0.6. The Hubble constant is chosen so that t(0) similar or equal to 13 Gyrs in all the models, while Ohm(b) = 0.02 h(2) is assumed for the baryon fraction. Clusters identified in the simulations are observed in projection so as to reproduce the main observational biases of the real data set. Clusters in the simulations are analysed by applying the same algorithm for interlopers removal and velocity dispersion estimate as for the reference observational sample. We find that a; for individual model clusters can be largely affected by observational biases, especially for sigma(nu) less than or similar to 600 km s(-1). The resulting effect of N(>sigma(nu)) is rather model dependent: models in which clusters had less time to virialize show larger discrepancies between intrinsic (3D) and projected distribution of velocity dispersions. From the comparison with real clusters we find that both SCDM and TCDM largely overproduce clusters. We verified for TCDM that agreement with the observational N(>sigma(nu)) requires sigma(8) = 0.5. As for the CHDM model, it marginally overproduces clusters and requires a somewhat larger sigma(8) value than a purely CDM model in order to produce the same cluster abundance. The Lambda CDM model with Ohm(0) = 0.3 agrees with data, while the open model with Ohm(0) = 0.4 and 0.6 underproduces and marginally overproduces clusters, respectively. (C) 1997 Elsevier Science B.V.