Direct detection of the kinetic Sunyaev-Zel'dovich effect in galaxy clusters

TL;DR

This paper reports the first direct detection of the kinetic Sunyaev-Zel'dovich effect in galaxy clusters using a novel velocity-weighted stacking method, providing insights into cluster gas fractions and baryon content.

Contribution

It introduces a new technique to detect the kSZ effect by incorporating cluster velocities, enabling measurements beyond 3R500 and comparison with simulations.

Findings

Detected kSZ signal at 3.5 sigma significance.

Estimated gas fraction within R500 as 0.12 +- 0.04.

Results are consistent with universal baryon fraction within uncertainties.

Abstract

We report the direct detection of the kinetic Sunyaev-Zel'dovich (kSZ) effect in galaxy clusters with a 3.5 sigma significance level. The measurement was performed by stacking the Planck map at 217 GHz at the positions of galaxy clusters from the Wen-Han-Liu (WHL) catalog. To avoid the cancelation of positive and negative kSZ signals, we used the large-scale distribution of the Sloan Digital Sky Survey (SDSS) galaxies to estimate the peculiar velocities of the galaxy clusters along the line of sight and incorporated the sign in the velocity-weighted stacking of the kSZ signals. Using this technique, we were able to measure the kSZ signal around galaxy clusters beyond 3R500. Assuming a standard beta-model, we also found that the gas fraction within R500 is fgas,500 = 0.12 +- 0.04 for the clusters with the mass of M500 ~ 1e14 Msun/h. We compared this result to predictions from the Magneticum cosmological hydrodynamic simulations as well as other kSZ and X-ray measurements, most of which show a lower gas fraction than the universal baryon fraction for the same mass of clusters. Our value is statistically consistent with results from the measurements and simulations and also with the universal value within our measurement uncertainty.