The X-ray/SZ view of the virial region. I. Thermodynamic properties. (arXiv:1301.0617v1 [astro-ph.CO])

The X-ray/SZ view of the virial region. I. Thermodynamic properties. (arXiv:1301.0617v1 [astro-ph.CO]):
We measure the thermodynamic properties of cluster outer regions to provide
constraints on the processes that rule the formation of large scale structures.
We derived the thermodynamic properties of the intracluster gas (temperature,
entropy) by combining the SZ thermal pressure from Planck and the X-ray gas
density from ROSAT. This method allowed us to reconstruct for the first time
temperature and entropy profiles out to the virial radius and beyond in a large
sample of objects. At variance with several recent Suzaku studies, we find that
the entropy rises steadily with radius, albeit at at a somewhat lower rate than
predicted by self-similar expectations. We note significant differences between
relaxed, cool-core systems and unrelaxed clusters in the outer regions. Relaxed
systems appear to follow the self-similar expectations more closely than
perturbed objects. Our results indicate that the well-known entropy excess
observed in cluster cores extends well beyond the central regions. When
correcting for the gas depletion, the observed entropy profiles agree with the
prediction from gravitational collapse only, especially for cool-core clusters.