Planck intermediate results XIII. Constraints on peculiar velocities

Using Planck data combined with the Meta Catalogue of X-ray detected Clusters of galaxies (MCXC), we address the study of peculiar motions by searching for evidence of the kinetic Sunyaev-Zeldovich effect (kSZ). By implementing various filters designed to extract the kSZ generated at the positions of the clusters, we obtain consistent constraints on the radial peculiar velocity average, root mean square (rms), and local bulk flow amplitude at different depths. For the whole cluster sample of average redshift 0.18, the measured average radial peculiar velocity with respect to the cosmic microwave background (CMB) radiation at that redshift, i.e., the kSZ monopole, amounts to 72 backslash pm 60backslash,kmbackslash,s^-1. This constitutes less than 1backslash,% of the relative Hubble velocity of the cluster sample with respect to our local CMB frame. From a subset of this cluster sample backslashPlanckbackslash finds the radial peculiar velocity rms to be below 800backslash,kmbackslash,s^-1 at the 95backslash,% confidence level, which is around three times the backslash LambdaCDM prediction for the typical cluster radial velocity rms at z=0.15. backslashPlanckbackslash data also set strong constraints on the local bulk flow in volumes centred on the Local Group. There is no detection of bulk flow as measured in any comoving sphere extending to the maximum redshift covered by the cluster sample. A blind search for bulk flows in this sample has an upper limit of 254backslash,kmbackslash,s^-1 (95backslash,% confidence level) dominated by CMB confusion and instrumental noise, indicating that the Universe is largely homogeneous on Gpc scales. In this context, in conjunction with supernova observations, backslashPlanckbackslash is able to rule out a large class of inhomogeneous void models as alternatives to dark energy or modified gravity. The backslashPlanckbackslash constraints on peculiar velocities and bulk flows are thus consistent with the backslash LambdaCDM scenario.