Neutralinos and the origin of radio halos in clusters of galaxies

We assume that the supersymmetric lightest neutralino is a good candidate f or the cold dark matter in the galaxy halo and explore the possibility to p roduce extended diffuse radio emission from high-energy electrons arising f rom the neutralino annihilation in galaxy clusters whose intracluster mediu m is filled with a large-scale magnetic field. We show that these electrons Dt the population of seed relativistic electrons that is postulated in man y models for the origin of cluster radio halos. For a uniform magnetic fiel d of approximate to1-3 muG the population of seed relativistic electrons fr om neutralino annihilation can Dt the radio halo spectra of two well-studie d clusters: Coma and 1E 0657-56. In the case of a magnetic field that is ra dially decreasing from the cluster center, central values approximate to8 m u \G (for Coma) and approximate to 50 muG (for 1E 0657-56) are required to fit the data. The radio halo data strongly favor a centrally peaked dark ma tter density profile (like a Navarro, Frenk, & White [NFW97] density profil e). The shape and the frequency extension of the radio halo spectra are con nected with the mass and physical composition of the neutralino. A pure gau gino neutralino with mass M chi greater than or equal to 80 GeV can reasona bly fit the radio halo spectra of both Coma and 1E 0657-56. The model we pr esent here provides a number of extra predictions that make it definitely t estable. On the one hand, it agrees quite well with the observations that ( 1) the radio halo is centered on the cluster dynamical center, usually coin cident with the center of its X-ray emission; (2) the radio halo surface br ightness is similar to the X-ray one; and (3) the monochromatic radio lumin osity at 1.4 GHz correlates strongly with the intracluster (IC) gas tempera ture. On the other hand, the same model predicts that radio halos should be present in every cluster, which is not presently observed, although the pr edicted radio halo luminosities can change (decrease) by factors of up to s imilar to 10(2)-10(6), depending on the amplitude and the structure of the IC magnetic field. In addition, neutral pions arising from neutralino annih ilation should give rise to substantial amounts of diffuse gamma-ray emissi on, up to energies of order M chi, that could be tested by the next-generat ion gamma-ray experiments.