Understand
The number density of galaxy clusters provides tight statistical constraints on the matter fluctuation power spectrum normalization, traditionally phrased in terms of sigma_8, the root mean square mass fluctuation in spheres with radius 8 h^-1 Mpc.
- We present constraints on sigma_8 and the total matter density Omega_m0 from local cluster counts as a function of X-ray temperature, taking care to incorporate and minimize systematic errors that plagued previous work with this method.
- In particular, we present new determinations of the cluster luminosity - temperature and mass - temperature relations, including their intrinsic scatter, and a determination of the Jenkins mass function parameters for the same mass definition as the mass - temperature calibration.
- Marginalizing over the 12 uninteresting parameters associated with this method, we find that the local cluster temperature function implies sigma_8 (Omega_m0/0.32)^alpha = 0.86+/-0.04 with alpha = 0.30 (0.41) for Omega_m0 < 0.32 (Omega_mo > 0.32) (68% confidence for two parameters).