On the Discrepancy between Theoretical and X-Ray Concentration-Mass
  Relations for Galaxy Clusters
  [Abridged] In the past 15 years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
has this relation been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
  We analyzed 52 objects, simulated each time with different physical recipes
for the baryonic component, as well as 60 synthetic X-ray images, to determine
if these discrepancies are real or artificial. In particular, we investigate
how the simulated concentration-mass relation depends (1) on the radial range
used to derive the concentration, (2) on the presence of baryons in the
simulations, and on the prescription used to reproduce the gas. Finally, we
evaluate (3) how the results differ when adopting an X-ray approach for the
analysis and (4) how the selection functions based on X-ray luminosity can
impact the results. All effects studied go in the direction of alleviating the
discrepancy between observations and simulations, although with different
significance: while the fitting radial range and the baryonic component play
only a minor role, the X-ray approach and selection function have profound
repercussion on the resulting concentration-mass relation.
