On the origin of central abundance drops in the intracluster medium of
  galaxy groups and clusters
  A central drop of ICM Fe abundance has been observed in several cool-core
clusters. It has been proposed that this abundance drop may be due, at least
partially, to the depletion of Fe into dust grains in the central, high-density
regions. According to this scenario, noble gas elements such as Ar and Ne are
not expected to be depleted into dust, and therefore should not show any drop,
but follow the general increase of metal abundance toward the center. In this
work, we test this scenario by measuring with {\sl Chandra} data the radial
profiles of Ar and Ne in a sample of 12 groups and clusters where a central
drop in Fe abundance has been detected. We confirm the presence of the Fe drop
in 10 out of 12 clusters at more than 2$\sigma$ c.l., and 4 Ar drops with
similar significance. We also find 4 Ne drops, with the caveat that Ne
abundance measurement from CCD spectra suffers from systematics not completely
under control. Our results are consistent with an abundance drop common to the
three elements. When comparing the profiles, we find that, on average, the
abundance profiles of Ar and Ne are significantly higher than Fe and steeper
toward the center, while they all gradually become consistent with solar
composition at $r\geq 0.05r_{500}$. We also check that Si and S profiles are
mostly consistent with Fe. This result confirms a scenario in which some
fraction of Fe is depleted into dust grains in the inner regions, although the
global central abundance drop is mostly due to mechanical processes, like the
displacement of metal-rich ICM from the very center to larger radii by
AGN-driven feedback. Finally, we report the detection of an Fe drop in the
cluster MACSJ1423.8+2404 at $z=0.543$, showing that this feature appears early
on in cool-core clusters.
