We report the direct detection of the kinetic Sunyaev-Zel'dovich (kSZ) effect in galaxy clusters with a 3.5σ 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 3 × R500. Assuming a standard β-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 ∼ 1.0 × 1014 h-1 M⊙. 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.
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Acknowledgements. The authors thank an anonymous referee for the useful comments and suggestions. This research has been supported by the funding for the ByoPiC project from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme grant agreement ERC-2015-AdG 695561. The authors acknowledge fruitful discussions with the members of the ByoPiC project (https://byopic.eu/team). Furthermore, S.Z. acknowledge support by the Israel Science Foundation (grant no. 255/18). We thank LSS2LSS science program of the Ψ2 initiative of the Institut Pascal, funded by the Paris-Saclay University, in which this research has been initiated. This publication used observations obtained with Planck (http://www.esa.int/Planck), an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada. The authors thank Klaus Dolag and Antonio Ragagnin for providing the Mag-neticum simulations, and Adi Nusser for fruitfull discussions.
© H. Tanimura et al. 2021.