The combination of measurements of the local abundance of rich clusters of galaxies and its evolution to higher redshift offers the possibility of a direct measurement of Omega_0 with little contribution from other cosmological parameters. We investigate the significance of recent claims that this evolution indicates that Omega_0 must be small. The most recent cluster velocity dispersion function (Girardi et al. 1997) from a compilation including the ESO Northern Abell Cluster Survey (ENACS) results in a significantly higher normalization for models, corresponding to sigma_8 approx 0.6 for Omega_0=1, compared to the Eke, Cole, & Frenk (1996) result of sigma_8=0.52 +/- 0.04. Using the ENACS data for a $z=0$ calibration results in strong evolution in the abundance of clusters, and we find that the velocity dispersion function is consistent with Omega_0=1. The results are dependent upon the choice and analysis of low-redshift and high-redshift data, so at present, the data is not good enough to determine Omega_0 unambiguously.
Large Scale Structure: Tracks and Traces
- Pub Date:
- 4 pages Latex using sprocl.sty, 1 figure. To appear in Proceedings of 12th Potsdam Cosmology Workshop, "Large-Scale Structure: Tracks and Traces" Sept. 15-19, 1997