A morphological comparison between giant radio halos and radio mini-halos in galaxy clusters

In this letter we present a morphological comparison between giant radio halos and radio mini-halos in galaxy clusters based on radio-X-ray luminosity, P1.4−LX, and radio luminosity-size, P1.4−RH, correlations. We report evidence that P1.4−LX and P1.4−RH trends may also exist for mini-halos: mini-halo clusters share the same region of giant halo clusters in the (P1.4, LX) plane, whereas they are clearly separated in the (P1.4,RH) plane. The synchrotron emissivity of mini-halos is found to be more than 50 times larger than that of giant halos, implying a very efficient process for their origins. By assuming a scenario of sporadical turbulent particle re-acceleration for both giant and mini halos, we discuss basic physical differences between these sources. Regardless of the origin of the turbulence, am ore efficient source of injection of particles, which eventually takes part in the re-acceleration process, is required in mini-halos, and this may result from the central radio galaxy or from proton-proton collisions in the dense cool core regions.