The full iron budget in simulated galaxy clusters: The chemistry between gas and stars

¹ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy
² IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34014 Trieste, Italy
³ Department of Physics; University of Michigan, 450 Church St, Ann Arbor, MI 48109, USA
⁴ Department of Physics, University of Trieste, Via G. Tiepolo 11, I-34131 Trieste, Italy
⁵ ICSC – Italian Research Center on High Performance Computing, Big Data and Quantum Computing, Via Magnanelli 2, 40033, Casalecchio di Reno, Italy
⁶ INFN – Istituto Nazionale di Fisica Nucleare, Via Valerio 2, I-34127, Trieste, Italy
⁷ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, Via A. Corti 12, I-20133 Milano, Italy
⁸ Universitäts-Sternwarte, Fakultüt für Physik, Ludwig-Maximilians-Universität München, Scheinerstr.1, 81679 München, Germany
⁹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany

^⋆ Corresponding author: veronica.biffi@inaf.it

Received: 15 November 2024
Accepted: 26 April 2025

Abstract

Context. Heavy chemical elements such as iron in the intra-cluster medium (ICM) of galaxy clusters are a signpost of the interaction between the gas and stellar components. Observations of the ICM metallicity in present-day massive systems, however, pose a challenge to the underlying assumption that the cluster galaxies have produced the amount of iron that enriches the ICM.

Aims. We evaluate the iron share between ICM and stars within simulated galaxy clusters with the twofold aim of investigating the origin of possible differences with respect to observational findings and of shedding light on the observed excess of iron on the ICM with respect to expectations based on the observed stellar population.

Methods. We evaluated the iron mass in gas and stars in a sample of 448 simulated systems with masses M_tot,500>10¹⁴ M_⊙ at z = 0.07. These were extracted from the high-resolution (352 h⁻¹ cMpc)³ volume of the MAGNETICUM cosmological hydrodynamical simulations. We compared our results with observational data of low-redshift galaxy clusters.

Results. The iron share in simulated clusters features a shallow dependence on the total mass, and its value is close to unity on average. In the most massive simulated systems, the iron share is thus smaller than observational values by almost an order of magnitude. The dominant contribution to this difference is related to the stellar component, whereas the chemical properties of the ICM agree well overall with the observations. We find larger stellar mass fractions in simulated massive clusters, which in turn yield higher stellar iron masses, than in observational data.

Conclusions. Consistently with the modelling, we confirm that the stellar content within simulated present-day massive systems causes the metal enrichment in the ICM. It will be crucial to alleviate the stellar mass discrepancy between simulations and observations to definitely assess the iron budget in galaxy clusters.