A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications

TL;DR

This paper measures large-scale bulk flows of galaxy clusters using X-ray and CMB data, finding flows that challenge standard cosmological models and suggest influence from pre-inflationary inhomogeneities.

Contribution

It provides the first large-scale measurement of galaxy cluster bulk flows using combined X-ray and WMAP data, revealing unexpected large-scale motions.

Findings

Detection of a strong, coherent bulk flow out to >300 h^{-1} Mpc

Bulk flow magnitude difficult to reconcile with LCDM predictions

Possible indication of pre-inflationary inhomogeneities affecting current horizon

Abstract

Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3-year WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least > 300 h^{-1} Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.