Speaker
Description
We present a study of the unresolved $\gamma$-ray background (UGRB) aimed at probing the nature of the faintest $\gamma$-ray source populations in the Universe. By leveraging statistical cross-correlations between the UGRB and tracers of large-scale structure, we assess the contributions of different source classes to this diffuse emission. Our analysis combines twelve years of Fermi Large Area Telescope (LAT) data with three years of Dark Energy Survey (DES) observations, focusing on the angular correlation between $\gamma$ rays and the galaxy distribution.
We detect a significant correlation with a signal-to-noise ratio of 7.85, dominated by large angular scales. To further constrain the origin of the signal, we perform a multi-tracer analysis incorporating the cross-correlation between $\gamma$ rays and DES weak lensing. The two independent probes are consistent, and their joint analysis increases the detection significance to 10.31, providing strong evidence for the predominantly extragalactic origin of the UGRB.
Interestingly, the inferred properties of the contributing sources differ from those of resolved $\gamma$-ray populations, indicating that the faint $\gamma$-ray sky cannot be explained by a straightforward extrapolation of known sources. These results highlight the power of cross-correlation techniques in uncovering the nature of unresolved cosmic backgrounds.
| Other topic / keywords: | Gamma-rays |
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