http://arxiv.org/abs/1911.11841
Cosmic rays in galaxy clusters are unique probes of energetic processes operating with large-scale structures in the Universe. Precise measurements of cosmic rays in galaxy clusters are essential for improving our understanding of non-thermal components in the intracluster-medium (ICM) as well as the accuracy of cluster mass estimates in cosmological analyses. In this paper, we perform a cross-correlation analysis with the extragalactic gamma-ray background and the thermal Sunyaev-Zel’dovich (tSZ) effect in the cosmic microwave background. The expected cross-correlation signal would contain rich information about the cosmic-ray-induced gamma-ray emission in the most massive galaxy clusters at $z\sim0.1-0.2$. We analyze the gamma-ray background map with 8 years of data taken by the Large Area Telescope onboard Fermi satellite and the publicly available tSZ map by Planck. Our measurements are consistent with a null detection, but a weak correlation is found at angular scales of $\sim10$ arcmins. The null detection in our cross-correlation analysis enables us to put the tightest constraint of the acceleration efficiency of cosmic ray protons at shocks. We find the acceleration efficiency must be below $2.4\%$ with a $2\sigma$ confidence level when the hydrostatic mass bias of clusters is assumed to be $30\%$, while our result is less affected by the assumed value of the hydrostatic mass bias. Our constraint implies that the non-thermal cosmic-ray pressure in the ICM can introduce only a $\le1\%$ level of the hydrostatic mass bias, highlighting that the cosmic ray is incompatible with the mass bias inferred by the Planck analyses. Finally, we discuss future detectability prospects of cosmic-ray-induced gamma rays from the Perseus cluster for the Cherenkov Telescope Array.
M. Shirasaki, O. Macias, S. Ando, et. al.
Thu, 28 Nov 19
70/70
Comments: 16 pages, 13 figures, 1 table
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