Evidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel’dovich Effect

Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel’dovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.

Figure 1

The upper panel shows the mean pairwise momentum estimator, Eq. (4), for the 5000 most luminous BOSS DR9 galaxies within the ACT sky region (red points), with bootstrap errors. The solid line is derived from numerical kSZ simulations [34] using a halo mass cutoff of $M_{200}=4.1\times {10}^{13}{M}_{\odot }$. The probability of the data given a null signal is $2.0\times {10}^{-3}$ including bin covariances. The lower panel displays the same sum but with randomized map positions, and is consistent with a null signal.