Galaxy clusters are optimal laboratories to test cosmology as well as models for physicaludprocesses acting on smaller scales. X–ray observations of the hot gas filling their darkudmatter potential well, i.e. the intra–cluster medium (ICM), still provides one of theudbest ways to investigate the intrinsic properties of clusters. Methods based on X–rayudobservations of the ICM are commonly used to estimate the total mass, assuming thatudthe gas traces the underlying potential well and satisfies spherical symmetry, and thermaludmotions dominate the total pressure support. However, non–thermal motions are likelyudto establish in the ICM, hence, contribute to the total pressure and have to be taken intoudaccount in the mass estimate.udIn this thesis I study the ICM thermo–dynamical structure by combiningudhydrodynamical simulations and synthetic X–ray observations of galaxy clusters. Theudmain goal is to study their gas velocity field and the implications due to non–thermaludmotions: first, by analysing directly the velocity patterns in simulated clusters and,udsecondly, by reconstructing the internal ICM structure from mock X–ray spectra. Toudthis aim, I developed and applied an X–ray photon simulator to obtain synthetic X–rayudspectra from the gas component in hydrodynamical simulations of galaxy clusters.udThe main findings of this work are as follows.ud(i) Ordered, rotational patterns in the gas velocity field in cluster cores can establishudduring the mass assembly process, but are found to be transient phenomena, easilyuddestroyed by passages of gas–rich subhaloes. This suggests that in smoothly growingudhaloes the phenomenon is in general of minor effect. Nonetheless, major mergers orudhighly disturbed systems can indeed develop significant ordered motions and rotation,udwhich contribute up to 20% to the total mass. (ii) It is indeed possible to reconstructudthe thermal structure of the ICM in clusters from X–ray spectral analysis, by recoveringudthe emission measure (EM) distribution of the gas as a function of temperature. This is possible with current X–ray telescopes (e.g. Suzaku) via multi–temperature fitting of X–udray spectra. (iii) High–precision X–ray spectrometers, such as ATHENA, will allow us toudmeasure velocity amplitudes of ICM non–thermal motions, from the velocity broadeningudof heavy–ion (e.g. iron) emission lines. In this work, these achievements are obtained byudapplying the virtual X–ray simulator to generate ATHENA synthetic spectra of simulatedudclusters. The non–thermal velocity of the ICM in the central region is used to furtherudcharacterise the cluster and the level of deviation from the expected self–similarity. Byudexcluding the clusters with the highest non–thermal velocity dispersion, the scatter of theudLX −T relation for the sample is significantly reduced, which will allow for a more preciseudcomparison between observations and simulations.
展开▼