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Register a new userThe chemical enrichment of the ICM from hydrodynamical simulations
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The study of the metal enrichment of the intra-cluster and inter-galactic media (ICM and IGM) represents a direct means to reconstruct the past history of star formation, the role of feedback processes and the gas-dynamical processes which determine the evolution of the cosmic baryons. In this paper we review the approaches that have been followed so far to model the enrichment of the ICM in a cosmological context. While our presentation will be focused on the role played by hydrodynamical simulations, we will also discuss other approaches based on semi-analytical models of galaxy formation, also critically discussing pros and cons of the different methods. We will first review the concept of the model of chemical evolution to be implemented in any chemo-dynamical description. We will emphasise how the predictions of this model critically depend on the choice of the stellar initial mass function, on the stellar life-times and on the stellar yields. We will then overview the comparisons presented so far between X-ray observations of the ICM enrichment and model predictions. We will show how the most recent chemo-dynamical models are able to capture the basic features of the observed metal content of the ICM and its evolution. We will conclude by highlighting the open questions in this study and the direction of improvements for cosmological chemo-dynamical models of the next generation.
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We present cosmological hydrodynamical simulations of galaxy clusters aimed at studying the process of metal enrichment of the intra--cluster medium (ICM). These simulations have been performed by implementing a detailed model of chemical evolution in the Tree-SPH gd code. This model allows us to follow the metal release from SNII, SNIa and AGB stars, by properly accounting for the lifetimes of stars of different mass, as well as to change the stellar initial mass function (IMF), the lifetime function and the stellar yields. As such, our implementation of chemical evolution represents a powerful instrument to follow the cosmic history of metal production. The simulations presented here have been performed with the twofold aim of checking numerical effects, as well as the impact of changing the model of chemical evolution and the efficiency of stellar feedback.
The uniformity of the intra-cluster medium (ICM) enrichment level in the outskirts of nearby galaxy clusters suggests that chemical elements were deposited and widely spread into the intergalactic medium before the cluster formation. This observational evidence is supported by numerical findings from cosmological hydrodynamical simulations, as presented in Biffi et al. (2017), including the effect of thermal feedback from active galactic nuclei. Here, we further investigate this picture, by tracing back in time the spatial origin and metallicity evolution of the gas residing at z=0 in the outskirts of simulated galaxy clusters. In these regions, we find a large distribution of iron abundances, including a component of highly-enriched gas, already present at z=2. At z>1, the gas in the present-day outskirts was distributed over tens of virial radii from the the main cluster and had been already enriched within high-redshift haloes. At z=2, about 40% of the most Fe-rich gas at z=0 was not residing in any halo more massive than 1e11 Msun/h in the region and yet its average iron abundance was already 0.4, w.r.t. the solar value by Anders & Grevesse (1989). This confirms that the in situ enrichment of the ICM in the outskirts of present-day clusters does not play a significant role, and its uniform metal abundance is rather the consequence of the accretion of both low-metallicity and pre-enriched (at z>2) gas, from the diffuse component and through merging substructures. These findings do not depend on the mass of the cluster nor on its core properties.
We review observations on the chemical enrichment of the intracluster medium (ICM) performed using BeppoSAX MECS data. The picture emerging is that non-cooling flow clusters have flat metallicity profiles, whereas a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content of the ICM. The observed abundance excess in the central regions of cooling flow clusters is probably due to metals ejected from the cD galaxy located in the cluster core. Cooling flow cluster have also enhanced Nickel abundances in their cores with respect to the non cooling flow clusters.
The nature of the Type Ia supernovae (SNIa) progenitors remains still uncertain. This is a major issue for galaxy evolution models since both chemical and energetic feedback play a major role in the gas dynamics, star formation and therefore in the overall stellar evolution. The progenitor models for the SNIa available in the literature propose different distributions for regulating the explosion times of these events. These functions are known as the Delay Time Distributions (DTDs). This work is the first one in a series of papers aiming at studying five different DTDs for SNIa. Here, we implement and analyse the Single Degenerate scenario (SD) in galaxies dominated by a rapid quenching of the star formation, displaying the majority of the stars concentrated in the bulge component. We find a good fit to both the present observed SNIa rates in spheroidal dominated galaxies, and to the [O/Fe] ratios shown by the bulge of the Milky Way. Additionally, the SD scenario is found to reproduce a correlation between the specific SNIa rate and the specific star formation rate, which closely resembles the observational trend, at variance with previous works. Our results suggest that SNIa observations in galaxies with very low and very high specific star formation rates can help to impose more stringent constraints on the DTDs and therefore on SNIa progenitors.
The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analyzing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the SPH GADGET-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large cluster-centric distances (~R180). In the outskirts, namely outside of ~0.2R180, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z>2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z=2 and z=0, across the entire radial range.
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