The physics inside the scaling relations for X-ray galaxy clusters: gas
  clumpiness, gas mass fraction and slope of the pressure profile
  In galaxy clusters, the relations between observables in X-ray and millimeter
wave bands and the total mass have normalizations, slopes and redshift
evolutions that are simple to estimate in a self-similar scenario. We study
these scaling relations and show that they can be efficiently expressed, in a
more coherent picture, by fixing the normalizations and slopes to the
self-similar predictions, and advocating, as responsible of the observed
deviations, only three physical mass-dependent quantities: the gas clumpiness
$C$, the gas mass fraction $f_g$ and the logarithmic slope of the thermal
pressure profile $\beta_P$. We use samples of the observed gas masses,
temperature, luminosities, and Compton parameters in local clusters to
constrain normalization and mass dependence of these 3 physical quantities, and
measure: $C^{0.5} f_g = 0.110 (\pm 0.002 \pm 0.002) \left( E_z M / 5 \times
10^{14} M_{\odot} \right)^{0.198 (\pm 0.025 \pm 0.04)}$ and $\beta_P = -d \ln
P/d \ln r = 3.14 (\pm 0.04 \pm 0.02) \left( E_z M / 5 \times 10^{14} M_{\odot}
\right)^{0.071 (\pm 0.012 \pm 0.004)}$, where both a statistical and systematic
error (the latter mainly due to the cross-calibration uncertainties affecting
the \cxo\ and \xmm\ results used in the present analysis) are quoted. The
degeneracy between $C$ and $f_g$ is broken by using the estimates of the
Compton parameters. Together with the self-similar predictions, these estimates
on $C$, $f_g$ and $\beta_P$ define an inter-correlated internally-consistent
set of scaling relations that reproduces the mass estimates with the lowest
residuals.
