Iron abundance distribution in the hot gas of merging galaxy clusters
  We present XMM-Newton/EPIC observations of six merging galaxy clusters and
study the distributions of their temperature, iron (Fe) abundance and
pseudo-entropy along the merging axis. For the first time, we focus
simultaneously, and in a comprehensive way, on the chemical and thermodynamic
properties of the freshly collided intracluster medium (ICM). The Fe
distribution of these clusters along the merging axis is found to be in good
agreement with the azimuthally-averaged Fe abundance profile in typical
non-cool-core clusters out to $r_{500}$. In addition to showing a moderate
central abundance peak, though less pronounced than in relaxed systems, the Fe
abundance flattens at large radii towards $\sim$0.2-0.3 $Z_\odot$. Although
this shallow metal distribution is in line with the idea that disturbed,
non-cool-core clusters originate from the merging of relaxed, cool-core
clusters, we find that in some cases, remnants of metal-rich and low entropy
cool cores can persist after major mergers. While we obtain a mild
anti-correlation between the Fe abundance and the pseudo-entropy in the (lower
entropy, $K$ = 200-500 keV cm$^2$) inner regions, no clear correlation is found
at (higher entropy, $K$ = 500-2300 keV cm$^2$) outer radii. The apparent
spatial abundance uniformity that we find at large radii is difficult to
explain through an efficient mixing of freshly injected metals, particularly in
systems for which the time since the merger is short. Instead, our results
provide important additional evidence in favour of the early enrichment
scenario - in which the bulk of the metals are released outside galaxies at $z$
> 2-3 - and extend it from cool-core and (moderate) non-cool-core clusters to a
few of the most disturbed merging clusters as well. These results constitute a
first step towards a deeper understanding of the chemical history of merging
clusters.
