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.

High-Significance Detection of Correlation Between the Unresolved Gamma-Ray Background and the Large Scale Cosmic Structure

DES and
FERMI-LAT

Collaborations

•

B. Thakore
(
- Turin U. and
- INFN, Turin and
- Munich U.
)

Jan 17, 2025

38 pages

e-Print:

2501.10506 [astro-ph.CO]

Report number:

FERMILAB-PUB-25-0018-PPD,
DES-2024-0866

Experiments:

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Abstract: (arXiv)

Our understanding of the

\gamma

-ray sky has improved dramatically in the past decade, however, the unresolved

\gamma

-ray background (UGRB) still has a potential wealth of information about the faintest

\gamma

-ray sources pervading the Universe. Statistical cross-correlations with tracers of cosmic structure can indirectly identify the populations that most characterize the

\gamma

-ray background. In this study, we analyze the angular correlation between the

\gamma

-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 (

\sim 10^{14} M_{\odot}

) and account for approximately 30-40 % of the UGRB above 10 GeV. Additionally, we observe a preference for a curved

\gamma

-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

gamma

-ray sources, such as star-forming galaxies or particle dark matter.

Note:

34 pages, 15 figures

References(85)

Figures(37)

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