The X-ray Cluster Normalization of the Matter Power Spectrum

TL;DR

This paper refines the measurement of the matter power spectrum normalization using local X-ray galaxy cluster data, carefully addressing systematic errors and combining results with WMAP5 data for improved cosmological constraints.

Contribution

It provides new calibrations of cluster relations and mass functions, and offers a systematic analysis of the matter fluctuation amplitude and density parameters.

Findings

sigma_8 (Omega_m0/0.32)^alpha = 0.86+/-0.04

Joint WMAP5 + cluster constraints: Omega_m0=0.30+/-0.03, sigma_8=0.85+/-0.04

No evidence of additional systematic errors in the method

Abstract

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). This result agrees with a wide range of recent independent determinations, and we find no evidence of any additional sources of systematic error for the X-ray cluster temperature function determination of the matter power spectrum normalization. The joint WMAP5 + cluster constraints are: Omega_m0 = 0.30+0.03/-0.02 and sigma_8 = 0.85+0.04/-0.02 (68% confidence for two parameters).