The Metal Content of the Hot Atmospheres of Galaxy Groups

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.

Simulating Groups and the IntraGroup Medium: The Surprisingly Complex and Rich Middle Ground between Clusters and Galaxies

“…The release of elements from stars is the source for the enrichment of the IGrM, about which an entire review by Gastaldello et al (2021) is written in this Special Issue "The Physical Properties of the Groups of Galaxies". In their Section 3.2, they include a discussion of chemical evolution models in cosmological hydrodynamic simulations.…”

The cycle of metals in the infalling elliptical galaxy NGC 1404

“…The lower abundance (and different profile shape) measured with 1T compared to multi-temperature modelling is expected: in fact, metallicities measured from CCDresolution spectra are well known to be underestimated if the temperature structure is modelled too simplistically with one component only (the so-called "Fe bias"; see e.g. Buote & Canizares 1994;Buote 2000;Mernier et al 2018a;Gastaldello et al 2021). It is interesting to note (and, in fact, remind) that this bias occurs even when one gas component dominates the other by one order of magnitude (see top right panel).…”

“…The case of lower mass systems, i.e. galaxy groups and early-type galaxies (ETGs), has been less studied and, consequently, less understood (for a recent review, see Gastaldello et al 2021). The intragroup medium (IGrM) and the hot, X-ray emitting atmosphere pervading elliptical galaxies are also rich in metals, detected essentially via the Fe-L complex; however the latter remains essentially unresolved at current CCD spectral resolution, making the Fe abundance more sensitive to systematics.…”

Properties of Fossil Groups of Galaxies

“…The hot intra-group gas contains elements that are typically synthesized in stars and SNe. For general details on this topic we refer the reader to the companion review of Gastaldello et al (2021). Here, we focus on the single study conducted on metal abundances in FGs, presented in Sato et al (2010).…”