The diffuse gamma-ray flux from clusters of galaxies

Saqib Hussain; Rafael Alves Batista; Elisabete M de Gouveia Dal Pino; Klaus Dolag

doi:10.1038/s41467-023-38226-w

The diffuse gamma-ray flux from clusters of galaxies

Nat Commun. 2023 Apr 29;14(1):2486. doi: 10.1038/s41467-023-38226-w.

Authors

Saqib Hussain^{1

2}, Rafael Alves Batista^{3

4}, Elisabete M de Gouveia Dal Pino⁵, Klaus Dolag^{6

7}

Affiliations

¹ Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG), University of São Paulo (USP), R. do Matão, 1226, 05508-090, São Paulo, Brazil. saqib.hussain@gssi.it.
² Gran Sasso Science Institute, Via Michele Iacobucci, 2, 67100, L'Aquila, Italy. saqib.hussain@gssi.it.
³ Instituto de Física Teórica UAM-CSIC, C/ Nicolás Cabrera 13-15, 28049, Madrid, Spain.
⁴ Departamento de Física Teórica, Universidad Autónoma de Madrid, M-15, 28049, Madrid, Spain.
⁵ Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG), University of São Paulo (USP), R. do Matão, 1226, 05508-090, São Paulo, Brazil.
⁶ University Observatory Munich, Scheinerstr. 1, 81679, München, Germany.
⁷ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str 1, 85741, Garching, Germany.

Abstract

The origin of the diffuse gamma-ray background (DGRB), the one that remains after subtracting all individual sources from observed gamma-ray sky, is unknown. The DGRB possibly encompasses contributions from different source populations such as star-forming galaxies, starburst galaxies, active galactic nuclei, gamma-ray bursts, or galaxy clusters. Here, we combine cosmological magnetohydrodynamical simulations of clusters of galaxies with the propagation of cosmic rays (CRs) using Monte Carlo simulations, in the redshift range z ≤ 5.0, and show that the integrated gamma-ray flux from clusters can contribute up to 100% of the DGRB flux observed by Fermi-LAT above 100 GeV, for CRs spectral indices α = 1.5 - 2.5 and energy cutoffs [Formula: see text] eV. The flux is dominated by clusters with masses 10¹³ ≲ M/M_⊙ ≲ 10¹⁵ and redshift z ≲ 0.3. Our results also predict the potential observation of high-energy gamma rays from clusters by experiments like the High Altitude Water Cherenkov (HAWC), the Large High Altitude Air Shower Observatory (LHAASO), and potentially the upcoming Cherenkov Telescope Array (CTA).