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

Abstract

Galaxy groups are more than an intermediate scale between clusters and halos hosting individual galaxies, they are crucial laboratories capable of testing a range of astrophysics from how galaxies form and evolve to large scale structure (LSS) statistics for cosmology. Cosmological hydrodynamic simulations of groups on various scales offer an unparalleled testing ground for astrophysical theories. Widely used cosmological simulations with ∼(100 Mpc)3 volumes contain statistical samples of groups that provide important tests of galaxy evolution influenced by environmental processes. Larger volumes capable of reproducing LSS while following the redistribution of baryons by cooling and feedback are the essential tools necessary to constrain cosmological parameters. Higher resolution simulations can currently model satellite interactions, the processing of cool (T≈104−5 K) multi-phase gas, and non-thermal physics including turbulence, magnetic fields and cosmic ray transport. We review simulation results regarding the gas and stellar contents of groups, cooling flows and the relation to the central galaxy, the formation and processing of multi-phase gas, satellite interactions with the intragroup medium, and the impact of groups for cosmological parameter estimation. Cosmological simulations provide evolutionarily consistent predictions of these observationally difficult-to-define objects, and have untapped potential to accurately model their gaseous, stellar and dark matter distributions.

Scaling relations of clusters and groups, and their evolution

“…The role of the AGN feedback in reproducing the observed properties of galaxy clusters have been confirmed in many other studies (e.g., McCarthy et al 2010, Fabjan et al 2010, Le Brun et al 2014, Gaspari et al 2014, McCarthy et al 2017. It is possible to obtain reasonable gas mass fractions with models without AGN feedback, but the f gas -T X relation is flatter than observed (see the reviews by Eckert et al 2021 andOppenheimer et al 2021 for more details). Reproducing the correct f gas -T X (or the M gas -M) relation is crucial for a proper comparison between observations and simulations.…”

“…Reproducing the correct f gas -T X (or the M gas -M) relation is crucial for a proper comparison between observations and simulations. The gas fraction is found to be mass-dependent (e.g., Vikhlinin et al 2006, Gonzalez et al 2007, Pratt et al 2009, Eckert et al 2016; see also the reviews by Eckert et al 2021 andOppenheimer et al 2021). A lower gas fraction leads to lower luminosity and Y X parameter impacting the shape of the relations.…”

The metal content of the hot atmospheres of galaxy groups

“…So far, the main limitation to study simulated groups of galaxies in more detail has been the lack of simulations within cosmological context able to consistently resolve and match the stellar and gas properties of massive galaxy clusters and galaxies, simultaneously. Groups, in this respect, have often rather served as crucial testbed for assessing the prediction power of physical models embedded into cosmological simulations, especially related to feedback from central galaxies (see the companion reviews by Oppenheimer et al (2021) and Eckert et al (2021)). Nonetheless, given the recent encouraging results obtained on the chemical and thermal properties of the diffuse gas in various cosmic structures, especially with improvements in the description of chemo-energetic feedback from galaxies in group and cluster cores, more dedicated studies specifically focusing on the group regime in cosmological simulations are definitely needed to explore the details of their formation and evolution.…”

“…Given their special position at the crossroad between smaller-scale physics and cosmic evolution, galaxy groups represent in fact a rather challenging, albeit crucial, target: capturing correctly the effects of feedback from central galaxies and BHs, given the shallower potential wells of groups compared to clusters, is of great importance. This has been in fact the main source of discrepancy in the comparison with observational findings, and consequently one of the crucial testbeds for cosmological simulations and the physical models therein included (for a thorough discussion, see the companion review by Oppenheimer et al, 2021).…”

“…The purpose of this paper is to review the status of the metal abundance measurements in the IGrM and the progress made by simulations to reproduce and interpret those measurements. It is a companion of the other reviews in this series addressing the scaling relations of these systems (Lovisari et al, 2021), the impact of AGN feedback (Eckert et al, 2021), the overall insight provided by simulations (Oppenheimer et al, 2021) and the properties of the particular class of fossil groups (Aguerri & Zarattini, 2021).…”