High-significance detection of correlation between the unresolved gamma-ray background and the large-scale cosmic structure

Thakore, B., Negro, M., Regis, M., Camera, S., Gruen, D., Fornengo, N., Roodman, A., Porredon, A., Schutt, T., Cuoco, A., Alarcon, A., Amon, A., Bechtol, K., Becker, M.R., Bernstein, G.M., Campos, A., Carnero Rosell, A., Carrasco Kind, M., Cawthon, R., Chang, C., Chen, R., Choi, A., Cordero, J., Davis, C., DeRose, J., Diehl, H.T., Dodelson, S., Doux, C., Drlica-Wagner, A., Eckert, K., Elvin-Poole, J., Everett, S., Ferté, A., Gatti, M., Giannini, G., Gruendl, R.A., Harrison, I. ORCID: https://orcid.org/0000-0002-4437-0770, Hartley, W.G., Huff, E.M., Jarvis, M., Kuropatkin, N., Leget, P.-F., MacCrann, N., McCullough, J., Myles, J., Navarro-Alsina, A., Pandey, S., Prat, J., Raveri, M., Rollins, R.P., Ross, A.J., Rykoff, E.S., Sánchez, C., Secco, L.F., Sevilla-Noarbe, I., Sheldon, E., Shin, T., Troxel, M.A., Tutusaus, I., Yanny, B., Yin, B., Zhang, Y., Aguena, M., Brooks, D., Carretero, J., da Costa, L.N., Davis, T.M., De Vicente, J., Desai, S., Doel, P., Flaugher, B., Frieman, J., García-Bellido, J., Gaztanaga, E., Gutierrez, G., Hinton, S.R., Hollowood, D.L., Honscheid, K., James, D.J., Kuehn, K., Lahav, O., Lee, S., Lima, M., Marshall, J.L., Mena-Fernández, J., Miquel, R., Ogando, R.L.C., Palmese, A., Pieres, A., Plazas Malagón, A.A., Samuroff, S., Sanchez, E., Sanchez Cid, D., Smith, M., Suchyta, E., Tarle, G., Vikram, V., Walker, A.R. and Weaverdyck, N. 2025. High-significance detection of correlation between the unresolved gamma-ray background and the large-scale cosmic structure. Journal of Cosmology and Astroparticle Physics 2025 (06) , 037. 10.1088/1475-7516/2025/06/037

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Abstract

Our understanding of the γ-ray sky has improved dramatically in the past decade, however, the unresolved γ-ray background (UGRB) still has a potential wealth of information about the faintest γ-ray sources pervading the Universe. Statistical cross-correlations with tracers of cosmic structure can indirectly identify the populations that most characterize the γ-ray background. In this study, we analyze the angular correlation between the γ-ray background and the matter distribution in the Universe as traced by gravitational lensing, leveraging more than a decade of observations from the Fermi-Large Area Telescope (LAT) and 3 years of data from the Dark Energy Survey (DES). We detect a correlation at signal-to-noise ratio of 8.9. Most of the statistical significance comes from large scales, demonstrating, for the first time, that a substantial portion of the UGRB aligns with the mass clustering of the Universe as traced by weak lensing. Blazars provide a plausible explanation for this signal, especially if those contributing to the correlation reside in halos of large mass (∼ 1014 M ⊙) and account for approximately 30–40% of the UGRB above 10 GeV. Additionally, we observe a preference for a curved γ-ray energy spectrum, with a log-parabolic shape being favored over a power-law. We also discuss the possibility of modifications to the blazar model and the inclusion of additional γ-ray sources, such as star-forming galaxies, misalinged active galactic nuclei, or particle dark matter.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	IOP Publishing
Date of First Compliant Deposit:	20 June 2025
Date of Acceptance:	26 April 2025
Last Modified:	20 Jun 2025 11:01
URI:	https://orca.cardiff.ac.uk/id/eprint/179234

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