Constraining the dark matter contribution of gamma rays in clusters of galaxies using Fermi-LAT data

Clusters of galaxies are the largest gravitationally bound systems in the Universe. Their dynamics are dominated by dark matter (DM), which makes them among the best targets for indirect DM searches. We analyze 12 years of data collected by the Fermi Large Area Telescope (Fermi-LAT) in the direction of 49 clusters of galaxies selected for their proximity to the Earth and their high x-ray flux, which makes them the most promising targets. We first create physically motivated models for the DM density around each cluster considering different assumptions for the substructure distribution. Then we perform a combined search for a gamma-ray signal in the Fermi-LAT data between 500 MeV and 1 TeV. We find a signal of gamma rays potentially associated with DM that is at a statistical significance of 2.5 sigma - 3.0 sigma when considering a slope for the subhalo mass distribution alpha = 1.9 and minimum mass of Mmin = 10-6M circle dot. The best-fit DM mass and annihi-lation cross sections for a bb over bar annihilation channel are m chi = 40-60 GeV and (sigma v) = (2-4) x 10-25 cm3/s. When we consider alpha= 2.0 and Mmin = 10-9M circle dot, the best fit of the cross section reduces to (sigma v) = (4-10) x 10-26 cm3/s. For both DM substructure models there is a tension between the values of (sigma v) that we find and the upper limits obtained with the nondetection of a gamma-ray flux from Milky Way dwarf spheroidal galaxies. This signalis thus more likely associated with gamma rays produced in the intracluster region by cosmic rays colliding with gas and photon fields.