Iron abundance distribution in the hot gas of merging galaxy clusters

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: i.urdampilleta@sron.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ MTA-Eötvös University Lendület Hot Universe Research Group, Pázmány Péter sétány 1/A, Budapest, 1117, Hungary
⁴ Institute of Physics, Eötvös University, Pázmány Péter sétány 1/A, Budapest 1117, Hungary
⁵ Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583, Japan
⁶ Department of Physics, Bogazici University, 34342 Istanbul, Turkey

Received: 12 March 2019
Accepted: 6 June 2019

Abstract

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 focused simultaneously, and in a comprehensive way, on the chemical and thermodynamic properties of the newly collided intra cluster 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 r₅₀₀. In addition to showing a moderate central abundance peak, though less pronounced than in relaxed systems, the Fe abundance flattens at large radii towards ∼0.2−0.3 Z_⊙. 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 cm²) inner regions, no clear correlation is found at (higher entropy, K = 500−2300 keV cm²) 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 toward a deeper understanding of the chemical history of merging clusters.