Deprojection of X-ray data in galaxy clusters: confronting simulations
  with observations
  Numerical simulations with varying realism indicate an emergent principle --
multiphase condensation and large cavity power occur when the ratio of the
cooling time to the free-fall time ($t_{\rm cool}/t_{\rm ff}$) falls below a
threshold value close to 10. Observations indeed show cool-core signatures when
this ratio falls below 20-30, but the prevalence of cores with \tctf~ratio
below 10 is rare as compared to simulations. In X-ray observations, we obtain
projected spectra from which we have to infer radial gas density and
temperature profiles. Using idealized models of X-ray cavities and multiphase
gas in the core and 3-D hydro jet-ICM simulations, we quantify the biases
introduced by deprojection based on the assumption of spherical symmetry in
determining $t_{\rm cool}/t_{\rm ff}$. We show that while the used methods are
able to recover the $t_{\rm cool}/t_{\rm ff}$ ratio for relaxed clusters, they
have an uncertainty of a factor of $2-3$ in systems containing large cavities
($\gtrsim 20$ kpc). We also show that the mass estimates from these methods, in
absence of X-ray spectra close to the virial radius, suffer from a degeneracy
between the virial mass ($M_{200}$) and the concentration parameter ($c$) in
the form of $M_{200}\: c^2 \approx$ constant. Additionally, lack of soft-X-ray
($\lesssim 0.5$ keV) coverage and poor spatial resolution make us overestimate
min($t_{\rm cool}/t_{\rm ff}$) by a factor of few in clusters with min($t_{\rm
cool}/t_{\rm ff}$) $\lesssim 5$. This bias can largely explain the lack of
cool-core clusters with min($t_{\rm cool}/t_{\rm ff}$) $\lesssim 5$.
