Cross-Correlation of the Extragalactic Gamma-ray Background with Luminous Red Galaxies

TL;DR

This study measures the cross-correlation between the extragalactic gamma-ray background and luminous red galaxies to constrain dark matter annihilation, finding no significant signal but setting upper limits and highlighting the potential of future surveys.

Contribution

It provides the first cross-correlation measurement between EGB and LRGs, constrains dark matter annihilation cross-sections, and assesses systematic uncertainties for future dark matter searches.

Findings

No significant cross-correlation detected.

Dark matter annihilation cross-section limits set for 10 GeV mass.

Systematic uncertainties are smaller than statistical errors.

Abstract

Measurements of the cross-correlation between the extragalactic gamma-ray background (EGB) and large-scale structure provide a novel probe of dark matter on extragalactic scales. We focus on luminous red galaxies (LRGs) as optimal targets to search for the signal of dark matter annihilation. We measure the cross-correlation function of the EGB taken from the Fermi Large Area Telescope with the LRGs from the Sloan Digital Sky Survey. Statistical errors are calculated using a large set of realistic mock LRG catalogs. The amplitude of the measured cross-correlation is consistent with null detection. Based on an accurate theoretical model of the distribution of dark matter associated with LRGs, we exclude dark matter annihilation cross-sections over $\langle \sigma v\rangle =3\times10^{-25}-10^{-26}\, {\rm cm}^3 \,{\rm s}^{-1}$ for a 10 GeV dark matter. We further investigate systematic effects due to uncertainties in the Galactic gamma-ray foreground emission, which we find to be an order of magnitude smaller than the current statistical uncertainty. We also estimate the contamination from astrophysical sources in the LRGs by using known scaling relations between gamma-ray luminosity and star-formation rate, finding them to be negligibly small. Based on these results, we suggest that LRGs remain ideal targets for probing dark matter annihilation with future EGB measurement and galaxy surveys. Increasing the number of LRGs in upcoming galaxy surveys such as LSST would lead to big improvements of factors of several in sensitivity.