Thermodynamical Properties of the ICM from Hydrodynamical Simulations

Abstract

Modern hydrodynamical simulations offer nowadays a powerful means to trace the evolution of the X-ray properties of the intra-cluster medium (ICM) during the cosmological history of the hierarchical build up of galaxy clusters. In this paper we review the current status of these simulations and how their predictions fare in reproducing the most recent X-ray observations of clusters. After briefly discussing the shortcomings of the self-similar model, based on assuming that gravity only drives the evolution of the ICM, we discuss how the processes of gas cooling and non-gravitational heating are expected to bring model predictions into better agreement with observational data. We then present results from the hydrodynamical simulations, performed by different groups, and how they compare with observational data. As terms of comparison, we use X-ray scaling relations between mass, luminosity, temperature and pressure, as well as the profiles of temperature and entropy. The results of this comparison can be summarised as follows: (a) simulations, which include gas cooling, star formation and supernova feedback, are generally successful in reproducing the X-ray properties of the ICM outside the core regions; (b) simulations generally fail in reproducing the observed "cool core" structure, in that they have serious difficulties in regulating overcooling, thereby producing steep negative central temperature profiles. This discrepancy calls for the need of introducing other physical processes, such as energy feedback from active galactic nuclei, which should compensate the radiative losses of the gas with high density, low entropy and short cooling time, which is observed to reside in the innermost regions of galaxy clusters.

Simulating the impact of dust cooling on the statistical properties of the intra-cluster medium

“…Indeed, Z = 0.3(t/t 0 )Z ⊙ normalised at 0.3Z ⊙ at z = 0 gives ∼ 0.2 at z = 0.5 and ∼ 0.1 at z = 1. However, observations as well as theoretical studies on the metal enrichment of the ICM have indicate high values of the metalicity, i.e Z ∼ 0.3Z ⊙ , up to redshift above 1 (Cora et al, 2008;Borgani et al, 2008). An early enrichment of the ICM/IGM with dust, then sputtered, could (partly) explain these high values of the metallicity.…”

“…The high metallicity observed in the intra-cluster medium (ICM hereafter -see for instance Borgani et al (2008), for recent works) is understood within analytical models and numerical simulations as a consequence of the various gravitational (galaxy-galaxy mergers, galaxy interactions, ram pressure stripping) and non-gravitational (SN powered galactic winds, AGN outbursts, starburts winds) processes at play in the ICM. These processes drive the formation and the evolution of galaxies within their environment (see for instance works by Kapferer et al (2006); Domainko et al (2006); Moll et al (2007).…”

On the ability of the spectroscopic Sunyaev-Zeldovich effect measurements to determine the temperature structure of galaxy clusters

“…These baryons accumulate in the cluster gravitational potential, which is dominated by cold dark matter and show, in their hotter phase (i.e. the hot intracluster medium -hereafter ICM -of temperature T e ∼ 10 7 −10 8 K), a complex temperature distribution in the cluster atmospheres as indicated by observations (see, e.g., Arnaud 2005, for a review; Pratt et al 2007, for XMM-Newton results; Ehlert & Ulmer 2009, for Chandra results; Sato et al 2009, for Suzaku results) and numerical simulations (see Borgani et al 2008, for a review).…”

The metal content of the hot atmospheres of galaxy groups

“…Many excellent reviews exist already focusing either on the more general topic of X-ray spectroscopy, mainly of the ICM, or directly on metal abundances both observationally and theoretically (Renzini, 2004(Renzini, , 2008Werner et al, 2008;Borgani et al, 2008;Böhringer & Werner, 2010;Kim, 2012;de Plaa, 2013;Mernier et al, 2018a;Biffi et al, 2018a) that ease our work which will then focus on the topics more directly related to the recent updates about metal abundances in galaxy groups. In this respect the only reviews of the topic are about the early history of the metal abundance measurements in the IGrM described in (Mulchaey, 2000) and a more recent update including the Chandra and XMM-Newton data can be found in (Sun, 2012).…”