Studying the Evolution of Cosmic Structure with Distant X-ray selected Clusters of Galaxies

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Galaxy clusters are ideal tracers of the cosmic large-scale structure and its growth rate as a function of time. This makes them prime probes for the test of cosmological models. They also form important laboratories to follow the evolution of galaxies and the baryonic intergalactic medium as a function of environmental conditions. They provide us with information on galaxy and star formation history and their effects on the intergalactic medium through heavy element pollution and entropy production. Whereas a good understanding of the present day cluster population is emerging, our knowledge of distant clusters and the cosmological implications of their properties is still sparse. X-ray observations are currently the best means to find massive distant galaxy clusters, because they display the clusters at high contrast.The growing archive of X-ray observations conducted with XMM-Newton provides the best available resource to conduct a survey for distant clusters, vastly superseding all similar efforts to date. Our survey project that exploits this unique opportunity to find at least 30 new clusters at z > 1 has now developed its full strength with the detection of already 5 clusters z > 1 and 5 close to redshift unity, more spectroscopic data in the pipeline and a reservoir of further candidates from our extensive XMM-Newton archive search and phomoteric follow-up program. These discoveries have supplied us with interesting study cases, provided first interesting insights and led to first publications. A large amount of work and follow-up observations are still required to reach the full goal of the project, a substantial part of which will be achieved within the coming funding period. We will be able to already address all the important points listed below.The final scientific goals of the project are (i) to characterize the large-scale structure evolution, to constrain cosmological model parameters, (ii) to obtain a statistical description of the evolution of the internal and structural properties of clusters, in particular information on the evolution of the observable-cluster mass relation, and (iii) to provide the basis for the evolutionary characterization of the cluster galaxy population and the intracluster plasma. The first studies have already confirmed that a pronounced sequence of old red galaxies still exists at redshifts around 1.4, and tight age constraints of cluster galaxies have been obtained for a System at z = 0.97. With the scheduled and planned follow-up observations we can now quite safely predict to get at least 15 clusters at z > 1 and more close to this limit. This will enable us to set tight constraints on the evolution of the X-ray luminosity function of clusters at these high redshifts and allow first approaches to cosmological tests before the completion of the project. Significant constraints on the nature of Dark Energy would come from a statistical subsample of about 10 of these clusters with deeper X-ray observations allowing a temperature and gas mass measurment, as already obtained for three of our detections. This depends on a ready success of proposals of deep X-ray observations for these clusters. Such data would also provide a very good overview on the history of heavy element enrichment of the ICM at high redshift.With the completion of the survey in progress covering about 40-50 square degrees (which will come shortly after the end of this funding period) we will have a unique and powerful sample size to get useful statistics on the scaling relations and on cosmological model tests. This project will act as a very important pathfinder for the upcoming large surveys of distant clusters using the Sunyaev-Zeldovich effect and later with eROSITA.