WMAP5 and the Cluster Mass Function

Abstract

The recently revised cosmological constraints from the Five-Year WMAP dataameliorate previous tension between cosmological constraints from the microwavebackground and from cluster abundances. We demonstrate that the revisedestimates of cosmological parameters are in excellent agreement with the massfunction of X-ray clusters in the Sloan Digital Sky Survey. Velocitysegregation between galaxies and the underlying dark matter could cause virialmass estimates to be biased, causing the mass scale of the mass function to beoffset from the true value. Modest velocity segregation($\sigma_{gxy}/\sigma_{DM}$=1.13$^{+0.06}_{-0.05}$) is sufficient to match themass function to the Five-Year WMAP results. When the new WMAP results arecombined 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 withexpectations for velocity segregation from state-of-the-art numericalsimulations of clusters. Together with the improved agreement between the newWMAP results and recent cosmic shear measurements, this result demonstratesthat the amplitude of large-scale structure in the nearby universe matches thatpredicted from the structure seen in the microwave background. The newconstraint we place on velocity segregation in clusters indicates that virialmass estimates for clusters are reasonably accurate. This result suggests thatfuture cluster surveys will be able to probe both cosmological parameters andfundamental cluster physics.