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Title: The effect of star formation and feedback on the X-ray properties of simulated galaxy clusters
Authors: Fabjan, Dunja
Supervisore/Tutore: Borgani, Stefano
Borgani, Stefano
Issue Date: 5-Mar-2010
Publisher: Università degli studi di Trieste
The aim of this Thesis was to study the X--ray properties of the IntraCluster Medium (ICM) in a cosmological context resorting to high resolution hydrodynamical simulations. The thermodynamical and chemical properties of the ICM were inspected and studied within a set of galaxy clusters that were simulated with the TREE-SPH Gadget2 code (Springel 2005). This code included a detailed model of chemical evolution (Tornatore et al. 2007) as well as prescriptions for different physical processes: star formation, galactic winds and AGN feedback.
We use this large set of simulated galaxy clusters with a twofold aim. First, we study the effect of different sources of feedback on the ICM observable properties, in particular on its metal enrichment and on thermo and chemo--dynamical properties when AGN feedback is at work. Second, we test the robustness of cluster mass proxies against the different physical processes included in the simulations.
When exploring the effect on metal enrichment and its evolution we found that among different prescriptions for the stellar Initial Mass Function (IMF), the best results on Iron abundance profiles and global Iron evolution are found when applying the Salpeter IMF (Salpeter 1955). We also found that the positive evolution of the metal abundance in the central regions of simulated clusters can not be simply interpreted as a consequence of an excess of low--redshift star formation. Instead the evolution of the metallicity pattern is driven by the combined action of gas--dynamical processes, which redistribute already enriched gas, and of star formation, which acts both as a source and as a sink of metals (Fabjan et al. 2008, Borgani et al. 2008).
Our analysis on the AGN feedback effect on ICM properties lends further support to the idea that a feedback source associated to gas accretion onto super-massive BHs is required by the observational properties of the ICM (e.g. McNamara & Nulsen 2007). However, our results also show that there are still a number of discrepancies between observations and the predictions made by simulations. This is especially true within the core regions of massive clusters, where a more efficient way of extracting and/or thermalising energy released by AGN is required. Our results further demonstrate that different astrophysical feedback sources leave distinct signatures on the pattern of chemical enrichment of the ICM. These differences are much more evident in the outskirts of galaxy clusters, which retain memory of the past efficiency that energy feedback had in displacing enriched gas from star-forming regions and in regulating star formation itself (Fabjan et al. 2010). The characterization of thermal and chemical properties in cluster external regions requires X--ray telescopes with large collecting area and an excellent control of the background, characteristics which should be eventually met by a future generation of X--ray satellites.
In the last part of this Thesis we studied the effect that different physical processes included in the simulations have on the mass--observable scaling relations and their evolution with redshift. We focused on two cluster mass proxies, the gas mass M_gas and a new Y_X proxy defined by Kravtsov et al. (2006) as the product of gas mass and cluster temperature and test the robustness of the two relations, M_tot-M_gas and M_tot-Y_X, in simulations before including any observational effect.
Furthermore we test the relations against the change of prescription for the physics that describes the ICM, such as viscosity, thermal conduction, star formation, galactic winds and AGN feedback. We found that the evolutions of both relations do not show any significant deviation from the predictions of the simple self--similar
model. However we found that the Y_X proxy is less sensitive to the change of physical processes included in simulations. Since Y_X is by definition a measure of the thermal pressure support in the ICM, once the central cluster region is excised, the relation M_tot-Y_X is more stable against the change of physical processes included in the simulations (Fabjan et al., in preparation).
In the future, the improved numerical resolution expected to be reached in simulations of the next generation needs to be accompanied by a suitable description of the subresolution physics, both concerning the star formation physics and and the AGN feedback. Within the latter, the inclusion of the jet injection by AGN would of course provide a physically meaningful description of the interplay between BH accretion and ICM properties. While Chandra, XMM and Suzaku will be pushed to their limits in these studies in the next few years, there is no doubt that a detailed knowledge of the ICM out the cluster virial boundaries and reaching very high redshift has to await for the advent of the next generation of X--ray telescopes (Giacconi et al. 2009, Arnaud et al.2009).
Ciclo di dottorato: XXII Ciclo
Keywords: CosmologiaAmmassi Di GalassieSimulazioni NumericheOsservazioni Banda XProprieta' ChimicheNuclei Galattici AttiviMezzo Intra ClusterCosmologyGalaxy clustersNumerical simulationsIntra Cluster MediumActive Galactic NucleiAbundancesX-ray astronomy
Type: Doctoral Thesis
Language: en
Settore scientifico-disciplinare: FIS/05 ASTRONOMIA E ASTROFISICA
NBN: urn:nbn:it:units-8819
Appears in Collections:Scienze fisiche

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