A volume-limited sample of X-ray galaxy groups and clusters: III.
  Central abundance drops
  We present the results of a search and study of central abundance drops in a
volume-limited sample (z<=0.071) of 101 X-ray galaxy groups and clusters. These
are best observed in nearby, and so best resolved, groups and clusters, making
our sample ideal for their detection. Out of the 65 groups and clusters in our
sample for which we have abundance profiles, 8 of them have certain central
abundance drops, with possible central abundance drops in another 6. All
sources with central abundance drops have X-ray cavities, and all bar one
exception have a central cooling time <=1 Gyr. These central abundance drops
can be generated if the iron injected by stellar mass loss processes in the
core of these sources is in grains, which then become incorporated in the
central dusty filaments. These, in turn, are dragged outwards by the bubbling
feedback process in these sources. We find that data quality significantly
affects the detection of central abundance drops, inasmuch as a higher number
of counts in the central 20 kpc of a source makes it easier to detect a central
abundance drop, as long as these counts are more than ~13000. On the other
hand, the magnitude of the central abundance drop does not depend on the number
of these counts, though the statistical significance of the measured drop does.
Finally, in line with the scenario briefly outlined above, we find that, for
most sources, the location of X-ray cavities acts as an upper limit to the
location of the peak in the radial metallicity distribution.
