Cross Correlating the Unresolved Gamma-Ray Background with Cosmic Large-Scale Structure from DESI: Implications for Astrophysics and Dark Matter

TL;DR

This paper forecasts the cross-correlation between the unresolved gamma-ray background and DESI galaxy data, demonstrating its potential to improve understanding of astrophysical sources and dark matter properties.

Contribution

It introduces a method to forecast the UGRB-galaxy cross-correlation signal, highlighting its significance for astrophysics and dark matter research.

Findings

High signal-to-noise ratio predicted for the cross-correlation, up to 20.6 for certain galaxy types.

Potential to measure UGRB flux evolution with 10% precision in some redshift bins.

Constraints on dark matter annihilation up to 300 GeV mass, three times stronger than current limits.

Abstract

The unresolved gamma-ray background (UGRB) is a diffuse gamma-ray emission arising from numerous extragalactic sources below the detection threshold and is an important component of the gamma-ray sky. Studying the UGRB is crucial for understanding high-energy astrophysical processes in the universe and for probing fundamental physics, such as the nature of dark matter. In this work, we forecast the cross-correlation between the UGRB and galaxy catalogs from the Dark Energy Spectroscopic Instrument (DESI) survey. First, we study the expected astrophysical contributions to the UGRB and their cross-correlation with DESI spectroscopic galaxies. Our calculations show that the cross-correlation signal-to-noise ratio is expected to be significant, with the highest value predicted to be 20.6 for DESI luminous red galaxies due to a higher predicted overlap in the redshift distribution with the UGRB. We consider two science cases that the UGRB-spectroscopic galaxies cross-correlation can be applied to: 1) measuring the UGRB flux as a function of redshift, achieving a precision of 10\% in some redshift bins, and 2) searching for annihilating dark matter potentially up to a mass of about 300~GeV, three times higher than the currently strongest constraints. This work underscores the importance of cross correlating the UGRB with cosmic large-scale structure tracers and highlights the multiwavelength approaches to advancing our understanding of high-energy astrophysical phenomena and fundamental physics.