Evidence of galaxy cluster rotation in the cosmic microwave background

TL;DR

This paper presents the first robust detection of the rotational kinematic Sunyaev-Zel'dovich effect in galaxy clusters, using combined CMB and galaxy redshift data, confirming theoretical predictions and opening new avenues for studying cluster dynamics.

Contribution

It provides the first robust observational evidence of the rkSZ effect in galaxy clusters, utilizing improved methods to isolate the signal from CMB noise and primary fluctuations.

Findings

Detected a dipolar rkSZ signature aligned with cluster rotation

Achieved 3.6 sigma confidence level in detection

Results are consistent with hydrodynamical simulation predictions

Abstract

We report the first robust evidence for the rotational kinematic Sunyaev-Zel'dovich (rkSZ) effect, produced by the Thomson scattering of cosmic microwave background (CMB) photons off rotating intracluster gas. By combining CMB intensity and polarization measurements from the $\it{Planck}$ satellite with spectroscopic member-galaxy redshifts from the Sloan Digital Sky Survey in a sample of 25 X-ray cross-matched, low-redshift ($0.02< z< 0.09)$, massive ($10^{13.9}\lesssim M_{\rm 500c}/M_\odot \lesssim 10^{14.6}$) galaxy clusters, we detect a dipolar rkSZ signature aligned with the estimated rotation direction of each cluster, ruling out a chance fluctuation at 99.98% confidence (3.6$\sigma$). The significance of this measurement is enhanced by several new methodological improvements for isolating the rkSZ signal from primary CMB fluctuations and noise. The amplitude and shape of the signal are qualitatively consistent with predictions from state-of-the-art hydrodynamical simulations. These results establish a new tool with which to probe the dynamical state of galaxy clusters using CMB data.