Multi-wavelength emissions from dark matter annihilation processes in galaxy clusters using cosmological simulations

Abstract

Based on the Marenostrum-MultiDark SImulation of galaxy Clusters (MUSIC-2) we develop semi-analytical models which provide multi-wavelength emission maps generated by dark matter (DM) annihilation processes in galaxy clusters and their sub-halos. We focus on radio and gamma-ray emission maps from neutralino DM annihilation processes testing two different neutralino masses, $\rm{M}_{\chi} = 35$ GeV and $60$ GeV along with two different models of the magnetic fields. A comparison of the radio flux densities from our DM annihilation model with the observed diffuse radio emission from the Coma cluster shows that they are of the same order of magnitude. We determine the DM densities with a Smoothed Particle Hydrodynamics (SPH) kernel. This enables us to integrate the DM annihilation signal along any given line of sight through the volume of the cluster. In particular it allows us to investigate the contribution of sub-halos to the DM annihilation signal with very high resolution. Zooming in on a subset of high mass-to-light ratio DM sub-halos, i.e. DM sub-halos with very low baryon content, we demonstrate that such targets can generate prominent annihilation signals. The radial distribution of high mass-to-light ratio (M/L) DM sub-halos is more strongly peaked at $\rm{R}_{200crit} \approx 1$ compared to the distribution of all sub-halos which may suggest that the search for DM annihilation signals from sub-halos in clusters is most promising at $\rm{R}_{200crit}$. The radio flux densities from DM sub-halos are well within the sensitivity limit of Square Kilometer Array (SKA) with an integration time of $1000$ hours and unlike clusters their gamma-ray spectrum is seen to be dominated by pion decay over a wide range of gamma-ray energies. Our model makes clear predictions for future radio and gamma-ray observations of the DM annihilation signal in clusters and their sub-halos.