Chemical Evolution on the Scale of Clusters of Galaxies: A Conundrum?
  The metal content of clusters of galaxies and its relation to their stellar
content is revisited making use of a cluster sample for which all four basic
parameters are homogeneously measured within consistent radii, namely
core-excised mass-weighted metallicity plus total, stellar and ICM masses. For
clusters of total mass $M_{500} >$ $\sim 10^{14}$ $M_{\odot}$ nice agreement is
found between their iron content and what expected from empirical supernova
yields. For the same clusters, there also appears to be at least as much iron
in the intracluster medium (ICM) as there is still locked into stars (i.e., the
ICM/stars metal share is about unity). However, for more massive clusters the
stellar mass fraction appears to drop substantially without being accompanied
by a drop in the ICM metallicity, thus generating a major tension with the
nucleosynthesis expectation and inflating the metal share to extremely high
values (up to $\sim 6$). Various possible solutions of this conundrum are
discussed, but are all considered either astrophysically implausible, or
lacking an independent observational support. For this reason we still
entertain the possibility that even some of the best cluster data may be
faulty, though we are not able to identify any obvious bias. Finally, based on
the stellar mass-metallicity relation for local galaxies we estimate the
contribution of galaxies to the ICM enrichment as a function of their mass,
concluding that even the most massive galaxies must have lost a major fraction
of the metals they have produced.
