The Metal Content of the Hot Atmospheres of Galaxy Groups

Fabio Gastaldello,Veronica Biffi,Aurora Simionescu,Massimo Gaspari,Francois Mernier,Kyoko Matsushita,Kosuke Sato

doi:10.3390/universe7070208

Abstract

Galaxy groups host the majority of matter and more than half of all the galaxies in the Universe. Their hot (107 K), X-ray emitting intra-group medium (IGrM) reveals emission lines typical of many elements synthesized by stars and supernovae. Because their gravitational potentials are shallower than those of rich galaxy clusters, groups are ideal targets for studying, through X-ray observations , feedback effects, which leave important marks on their gas and metal contents. Here, we review the history and present status of the chemical abundances in the IGrM probed by X-ray spectroscopy. We discuss the limitations of our current knowledge, in particular due to uncertainties in the modeling of the Fe-L shell by plasma codes, and coverage of the volume beyond the central region. We further summarize the constraints on the abundance pattern at the group mass scale and the insight it provides to the history of chemical enrichment. Parallel to the observational efforts, we review the progress made by both cosmological hydrodynamical simulations and controlled high-resolution 3D simulations to reproduce the radial distribution of metals in the IGrM, the dependence on system mass from group to cluster scales, and the role of AGN and SN feedback in producing the observed phenomenology. Finally, we highlight future prospects in this field, where progress will be driven both by a much richer sample of X-ray emitting groups identified with eROSITA, and by a revolution in the study of X-ray spectra expected from micro-calorimeters onboard XRISM and ATHENA.

Highlights

This article is an open access articleTwo major astrophysical discoveries have provided key answers to the fundamental question of the origin of the chemical elements in the past century: the discovery that stellar nucleosynthesis is responsible for the production of all the heavy elements from lithium to uranium [1,2,3] and the detection of line emission due to highly ionized iron in the X-ray spectra of the intra-cluster medium (ICM) [4,5]
As for the non-gravitational effect, such as AGN feedback, the entropy profiles are a good probe to estimate for each group and cluster, and we describe it in the following paragraph
While waiting for the exploitation of micro-calorimeters onboard XRISM and Athena, one should keep in mind the valuable potential of the Reflection Grating Spectrometer (RGS)

Summary

Introduction

Two major astrophysical discoveries have provided key answers to the fundamental question of the origin of the chemical elements in the past century: the discovery that stellar nucleosynthesis is responsible for the production of all the heavy elements from lithium to uranium [1,2,3] and the detection of line emission due to highly ionized iron in the X-ray spectra of the intra-cluster medium (ICM) [4,5]. The impact of these two distributed under the terms and conditions of the Creative Commons. The improvements in the stellar and supernova nucleosynthesis theory and modelization (e.g., References [6,7] and references therein) established that the major astrophysical sources of the chemical elements are: (i) Core-collapse supernovae (SNcc) and their massive progenitors (&8–10 M ) synthesize most of the O, Ne, and Mg of the Universe and a considerable fraction of Si and S (collectively called α elements as they are the result of fusion process involving the capture of α particles); (ii) Type Ia supernovae (SNIa), whose progenitors are generally believed to be exploding white dwarfs in binary systems, synthesize Ar, Fe, and the other Fe-peak elements, such as Cr and Ni, and the remaining fraction of Si and S; (iii) Asymptotic giant branch (AGB) stars produce mainly C, N which are ejected through stellar winds

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