Multi-frequency analysis of neutralino dark matter annihilations in the Coma cluster

Abstract

We study the astrophysical implications of neutralino dark matter annihilations in galaxy clusters, with a specific application to the Coma cluster. We first address the determination of the dark halo models for Coma, starting from structure formation models and observational data, and we discuss in detail the role of sub-halos. We then perform a thorough analysis of the transport and diffusion properties of neutralino annihilation products, and investigate the resulting multi-frequency signals, from radio to gamma-ray frequencies. We also study other relevant astrophysical effects of neutralino annihilations, like the DM-induced Sunyaev-Zel'dovich effect and the intracluster gas heating. As for the particle physics setup, we adopt a two-fold approach, resorting both to model-independent bottom-up scenarios and to benchmark, GUT-motivated frameworks. We show that the Coma radio-halo data (the spectrum and the surface brightness) can be nicely fitted by the neutralino-induced signal for peculiar particle physics models and for magnetic field values, which we outline in detail. Fitting the radio data and moving to higher frequencies, we find that the multi-frequency spectral energy distributions are typically dim at EUV and X-ray frequencies (with respect to the data), but show a non-negligible gamma-ray emission, depending on the amplitude of the Coma magnetic field. A simultaneous fit to the radio, EUV and HXR data is not possible without violating the gamma-ray EGRET upper limit. The best-fit particle physics models yields substantial heating of the intracluster gas, but not sufficient energy injection as to explain the quenching of cooling flows in the innermost region of clusters. Due to the specific multi-frequency features of the DM-induced spectral energy distribution in Coma, we find that supersymmetric models can be significantly and optimally constrained either in the gamma-rays or at radio and microwave frequencies.