On the occurrence of 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. An unbiased study of the
statistical properties of RHs is crucial to constrain their origin and
evolution. We aim at investigating the occurrence of RHs and its dependence on
the cluster mass in a SZ-selected sample of galaxy clusters, which is as close
as possible to be a mass-selected sample. Moreover, we analyse the connection
between RHs and merging clusters. We select from the Planck SZ catalogue
(Planck Collaboration XXIX 2014) clusters with $M\geq 6\times10^{14} M_\odot$
at z=0.08-0.33 and we search for the presence of RHs using the NVSS for z<0.2
and the GMRT RH survey (GRHS, Venturi et al. 2007, 2008) and its extension
(EGRHS, Kale et al. 2013, 2015) for 0.2<z<0.33. We use archival Chandra X-ray
data to derive information on the clusters dynamical status. We confirm that RH
clusters are merging systems while the majority of clusters without RH are
relaxed, thus supporting the idea that mergers play a fundamental role in the
generation of RHs. We find evidence for an increase of the fraction of clusters
with RHs with the cluster mass and this is in line with expectations derived on
the basis of the turbulence re-acceleration scenario. Finally, we discuss the
effect of the incompleteness of our sample on this result.
