Abstract

We are experiencing a unique epoch in the history of galaxy cluster studies. We have now open windows across the whole electromagnetic spectrum which offer us complementary approaches for cluster detection and analyses. Almost forty years after its theoretical prediction, first large radio telescopes started to scan the sky looking for massive clusters as "shadows" in the cosmic microwave background imprinted there by their hot gas content via the Sunyaev-Zel'dovich effect (SZE). In X-rays this hot plasma can be observed also directly. Optical and infrared telescopes give us a view on the galaxy population of clusters and through gravitational lensing also on its dominant, invisible component - the dark matter. The advent of multi-wavelength cluster surveys brings also the necessity to compare and cross-calibrate each cluster detection approach. This is the main aim of this work carried out in the framework of the XMM-\emph{Newton}-Blanco Cosmology Survey project (XMM-BCS). This project is a coordinated multi-wavelength survey in a 14~deg$^2$ test region covered in the optical band by the Blanco Cosmology Survey, in the mid-infrared by the \emph{Spitzer} Space Telescope and in X-rays by XMM-\emph{Newton}. This area is also part of the sky scanned by both SZE survey instruments: the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT). In the first part of the thesis I describe the analysis of the initial 6~deg$^2$ core of the X-ray survey field. From the detected extended sources a cluster catalog comprising 46 objects is constructed. These cluster candidates are confirmed as significant galaxy overdensities in the optical data, their photometric redshifts are measured and for a subsample confirmed with spectroscopic measurements. I provide physical parameters of the clusters derived from X-ray luminosity and carry out a first comparison with optical studies. The cluster catalog will be useful for direct cross-comparison with optical/mid-infrared catalogs, for the investigation of the survey selection functions, stacking analysis of the SZE signal and for cosmological analyses after combing with clusters detected in the extension of the survey. The extension of the survey to 14~deg$^2$ is a first scientific utilization of the novel XMM-\emph{Newton} mosaic mode observations. I have developed a data analysis pipeline for this operation mode and report on the discovery of two galaxy clusters, SPT-CL~J2332-5358 and SPT-CL~J2342-5411, in X-rays. The clusters were also independently detected through their SZE signal by the SPT and in the optical band in the BCS data. They are thus the first clusters detected under survey conditions by all major cluster search approaches. This work also demonstrates the potential of the mosaic mode observations to effectively cover large sky areas and detect massive clusters out to redshifts $\sim1$ even with shallow exposures. The last part of the thesis provides an example of a multi-wavelength analysis of two high-redshift ($z>1$) systems in the framework of the XMM-\emph{Newton} Distant Cluster Project. With the detection and studies of these high redshift systems we are for the first time able to see the assembly phase of the galaxy population of the clusters, which in nearby systems is totally passive, but at these high redshifts still show signatures of star formation.