Radio halos in galaxy clusters: insight from a mass-selected sample

Giant Radio Halos (RH) are diffuse Mpc-scale synchrotron sources detected in a fraction of massive and merging galaxy clusters. The currently prevailing picture is that RHs trace turbulent regions in the ICM where particles are trapped and accelerated. This scenario predicts a tight connection between the RH properties and the mass and dynamics of the hosting cluster. Large mass-selected samples of galaxy clusters are necessary to explore this connection. We used the Planck SZ cluster catalogue to build up an almost mass-selected sample of galaxy clusters with M > 6×1014MΘ and z=0.08-0.33. We looked for the presence of RHs in these clusters in the NVSS at z<0.2 and in the Extended GMRT Radio Halo Survey at z>0.2. We found evidence of a drop of the fraction of clusters with RHs at lower masses and we confirmed that RHs are generated in merging systems, supporting the idea that mergers play a key role in the formation of RHs. In this respect the next years will be crucial for the understanding of the origin and evolution of RHs, since the new generation of radio telescopes (e.g. LOFAR, MWA, ASKAP) will survey the sky with an unprecedented sensitivity and resolution allowing to test the models in a totally unexplored range of frequencies, RH luminosities, redshift and cluster masses.