WMAP5 and the Cluster Mass Function

TL;DR

The paper shows that revised WMAP5 data align well with cluster mass functions, and that velocity segregation effects are small, supporting the accuracy of cluster mass estimates and the consistency of large-scale structure measurements.

Contribution

It demonstrates the agreement between WMAP5 cosmological constraints and cluster mass functions, and constrains velocity segregation effects in galaxy clusters.

Findings

Revised WMAP5 data agree with SDSS X-ray cluster mass function.

Modest velocity segregation explains the mass function alignment.

Future cluster surveys can effectively probe cosmology and cluster physics.

Abstract

The recently revised cosmological constraints from the Five-Year WMAP data ameliorate previous tension between cosmological constraints from the microwave background and from cluster abundances. We demonstrate that the revised estimates of cosmological parameters are in excellent agreement with the mass function of X-ray clusters in the Sloan Digital Sky Survey. Velocity segregation between galaxies and the underlying dark matter could cause virial mass estimates to be biased, causing the mass scale of the mass function to be offset from the true value. Modest velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.13$^{+0.06}_{-0.05}$) is sufficient to match the mass function to the Five-Year WMAP results. When the new WMAP results are combined with constraints from supernovae and baryon acoustic oscillations, there is no need for velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.05$\pm$0.05). This result agrees with expectations for velocity segregation from state-of-the-art numerical simulations of clusters. Together with the improved agreement between the new WMAP results and recent cosmic shear measurements, this result demonstrates that the amplitude of large-scale structure in the nearby universe matches that predicted from the structure seen in the microwave background. The new constraint we place on velocity segregation in clusters indicates that virial mass estimates for clusters are reasonably accurate. This result suggests that future cluster surveys will be able to probe both cosmological parameters and fundamental cluster physics.