Cross-correlation of the extragalactic gamma-ray background with the thermal Sunyaev-Zel’dovich effect in the cosmic microwave background

Abstract

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 nonthermal 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-Zeldovich (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 ∼ 0.1-0.2. 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. We confirm that the measured crosscorrelation is consistent with a null detection, and thus it enables us to put the tightest constraint on the acceleration efficiency of cosmic-ray protons at shocks in and around galaxy clusters. We find the acceleration efficiency must be below 5% with a 2σ confidence level when the hydrostatic mass bias of clusters is assumed to be 30%, and our result is not significantly affected by the assumed value of the hydrostatic mass bias. Our constraint implies that the nonthermal cosmic-ray pressure in the ICM can introduce only a ≲3% level of the hydrostatic mass bias, highlighting that cosmic rays alone do not account for 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.

An EAGLE view of the missing baryons

“…Nonetheless, while cosmic rays could potentially change the thermal structure of the CGM around the galaxies they are expelled from, the extent of these rays is limited. Indeed, crosscorrelation of the extragalactic gamma-ray background with SZ maps imply that cosmic rays cannot affect for a significant fraction of the total pressure in clusters of galaxies (Shirasaki et al 2020). Thus, cosmic rays are not expected to alter the intergalactic gas studied here.…”

Astrophysical and Cosmological Probes of Dark Matter

“…Progress will therefore be critically reliant on new insights for how to exploit the data. This is happening on many fronts, including identifying new objects in which to search for dark matter signals, such as newly discovered Milky Way dwarfs [78][79][80][81][82][83], galaxy cata-Snowmass2021 Theory Frontier: Astrophysical and Cosmological Probes of Dark Matter logs [84,85], or dark substructure [86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105], as well as the development of techniques such as cross correlation with different datasets [106][107][108][109][110][111][112][113], improvements in our modeling of diffuse backgrounds [114][115][116][117], the extension to axion searches as we describe in Sec. 2.4, and the exploitation of the dark matter brightness of the ambient Milky Way [32,[118][119][120].…”