Entropy Flattening, Gas Clumping and Turbulence in Galaxy Clusters
  Several physical processes and formation events are expected in cluster
outskirts, a vast region up to now essentially not covered by observations. The
recent Suzaku (X-ray) and Planck (Sunayev-Zeldovich effect) observations out to
the virial radius have highlighted in these peripheral regions a rather sharp
decline of the intracluster gas temperature, an entropy flattening in contrast
with the theoretically expected power law increase, the break of the
hydrostatic equilibrium even in some relaxed clusters, a derived gas mass
fraction above the cosmic value measured from several CMB experiments, and a
total X-ray mass lower than the weak lensing mass determinations. Here we
present the analysis of four clusters (A1795, A2029, A2204 and A133) with the
SuperModel that includes a nonthermal pressure component due to turbulence to
sustain the hydrostatic equilibrium also in the cluster outskirts. In such way
we obtain a correct determination of the total X-ray mass and of the gas mass
fraction; this in turn allows to determine the level of the gas clumping that
can affect the shape of the entropy profiles reported by the Suzaku
observations. Our conclusion is that the role of the gas clumping is very
marginal and that the observed entropy flattening is due to the rapid decrement
of the temperature in the cluster outskirts caused by non gravitational
effects. Moreover, we show that the X-ray/SZ joint analysis from ROSAT and
Planck data, as performed in some recent investigations, is inadequate to
discriminate between a power law increase and a flattening of the entropy.
