The diffuse gamma-ray flux from clusters of galaxies

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 $${E}_{\max }=1{0}^{16}-1{0}^{17}$$ E max = 1 0 16 − 1 0 17 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).

Constraining Baryon Loading Efficiency of Active Galactic Nuclei with Diffuse Neutrino Flux from Galaxy Clusters

“…We note that the diffuse neutrino flux from the galaxy cluster highly depends on model parameters such as the baryon loading factor η p,grav and others. In the previous literature (Fang & Olinto 2016;Fang & Murase 2018;Hussain et al 2023), the authors aim to explore the potential of galaxy clusters as the major sources of the all-sky diffuse high-energy neutrino flux, so they tune the model parameters to make the predicted neutrino flux match the measured one. The latest observational upper limits of the diffuse neutrino flux from galaxy clusters presented by IceCube in Abbasi et al (2022) suggest that the contribution of the galaxy cluster population with masses between 10 14 M e and 10 15 M e cannot exceed 9%-13% of the diffuse flux, which can thus be also used to constrain the model parameters in previous literature, as we do in the present study.…”

“…The upper limits of baryon loading factor η p,grav constrained by diffuse muon-neutrino and γ-ray flux with different indices α of the injected protons from 2.0 to 2.5. (Fang & Murase 2018;Hussain et al 2023). However, the origin of the IGRB is still under debate; besides the galaxy clusters, the observed IGRB is possibly superimposed by different populations of γ-ray emitters, such as star-forming galaxies, starburst galaxies, and AGNs.…”

“…As a result, the aforementioned uncertainties may not be so severe. Another uncertainty arises from the accuracy of the EBL model, which may affect the attenuated γ-ray spectrum (Hussain et al 2023).…”

Neutrinos and Gamma Rays from Galaxy Clusters Constrained by the Upper Limits of IceCube

“…Several studies (see, e.g., Murase et al 2013;Fang & Olinto 2016;Fang & Murase 2018;Hussain et al 2021Hussain et al , 2023 have predicted that clusters of galaxies can contribute to a sizable percentage to the diffuse neutrino and γ-ray background. In particular, Hussain et al (2021Hussain et al ( , 2023) used the most detailed numerical approach to date combining three-dimensional (3D) cosmological magnetohydrodynamic (MHD) simulations with Monte Carlo simulations of CR propagation and cascading and predicted that clusters can potentially contribute to a fairly large fraction of the diffuse neutrino and γ-ray background observed by IceCube (Aartsen et al 2015a) and Fermi-LAT (Ackermann et al 2015), respectively. However, the aforementioned upper limit reported by the IceCube (Abbasi et al 2022) excludes part of the parametric space they considered in their analysis of the neutrino flux.…”

“…However, the aforementioned upper limit reported by the IceCube (Abbasi et al 2022) excludes part of the parametric space they considered in their analysis of the neutrino flux. 4 In this work, we constrain the parametric space considered in Hussain et al (2021Hussain et al ( , 2023 employing the latest upper limits reported by the IceCube for the neutrino flux of galaxy clusters and derive new limits to the diffuse γ-ray flux. We find that these new constraints eliminate the harder CR spectral indices α  2.0, but still predict a substantial contribution from the clusters to the very-high-energy range of the γ-ray flux.…”