SCIENTIFIC RATIONALE

Models of hierarchical galaxy and structure formation predict that mass is assembled inhomogeneously along filaments, forming a cosmic web. In the past decade, huge efforts have been dedicated to studying these nodes: clusters of galaxies which trace the most massive dark matter halos and their components such as galaxies, intracluster medium and dark matter.

Investigating these objects - and their members - in detail will drastically increase our insight into the assembly of galaxy clusters. Cluster galaxies are prime laboratories for the accelerated built-up of massive galaxies and enables us to characterize the role environment plays on the formation and evolution of galaxies. Thus, we can test current cosmological formation models with the earliest seeds of cluster formation. A crucial epoch for galaxy evolution and formation are the first billion years of the universe (beyond redshift z=1) coming along with an enhanced star-formation and black hole activity compared to the local universe and a huge growth of stellar mass both in cluster and field galaxies.

Strikingly, theoretical predictions estimate a factor of 5-10 lower star formation rate densities than observed in the FIR-submm-radio window, suggesting that a revision of feedback and star formation mode recipes is needed. Thus, a comparison of observations and numerical cosmological simulations (comprising hydro-dynamical, semi-analytical and abundance-matching approaches/methods) is indispensable in order to refine/adjust simulations (and their accuracies) and selection techniques

Beside the significant recent advances in this research area there are still several key questions that remain open: i) which of the present-day cluster (massive) galaxies formed at high redshift? ii) when and how present-day galaxy clusters formed in the distant universe? iii) are the overall properties of large-scale structures consistent with model predictions? and iv) how does galaxy environment affect the conversion of molecular gas into stars?

Over the past two decades a large variety of selection techniques and tools have been developed to search for clusters at different redshifts and evolutionary stages. These techniques span the whole electromagnetic spectrum and are sensitive to different physical properties and effects and produced a so-called „(proto)cluster zoo“. The number of known protoclusters (clusters in formation) beyond z=2 is still small. Naturally, this introduces substantial uncertainties, incompleteness and selection bias in our findings. With the advance of space missions and the upgrade respectively the construction of next generation ground-based telescopes/instruments, the situation will change completely and will break several frontiers at once such as extending from single digits to several hundred to thousands of cluster systems in formation, and getting systematics in the highly heterogenous sample of clusters in the distant universe.

This symposium will focus on two key topics in this research field: i) protocluster assembly and protocluster searches and ii) star formation in clusters across cosmic time. The contributions will be based both on observational and theoretical studies spanning the whole range of the electromagnetic spectrum.