  The concentration-mass relations proposed by Prada et al. (2012) and by Duffy
et al. (2008) on the scales of galaxy clusters show some of the largest
discrepancies among all the works present in literature. This is surprising
because they are both derived from the analysis of dark-matter halos forming in
LCDM simulations with similar set-ups. With the help of analytic models and
numerical simulations we investigate the origin of this discrepancy focusing on
the procedures used to derive the concentrations (circular velocity ratios
versus density profile fitting) and on the selection criteria used to bin the
halos (binning in maximum circular velocity versus binning in mass). We find
that both steps of the analysis have a large impact on the resulting c-M
relation. In particular, we show that the two c-M relations can be entirely
reconciled, if we account for these methodological differences. Our analysis
demonstrates that the concentration estimates are sensitive to the largely
different radial scales probed by a particular measurement method. This implies
that concentrations derived with different techniques (both in observations and
in simulations) must be compared over the same radial range.

Cosmology and Nongalactic Astrophysics