Title: Caught in the Spiderweb
Abstract: Within the framework of the hierarchical growth of large-scale structures in the universe, mass is assembled inhomogeneously along walls and filaments which forms a "cosmic web", galaxy clusters are formed at intersections of such filaments. Galaxy protoclusters (galaxy clusters in formation) are expected to contribute significantly to the star-formation rate density in the distant universe, thus understanding how clusters assembled their mass in the early universe is of critical importance. Over the last decade, a growing number of studies have identified galaxy protoclusters in the early universe through various techniques. The Spiderweb protocluster is a spectacular example of such high-z structures and stands out as one of the most massive and best studied systems at z>2 both in terms of its galaxy populations and large-scale structure, with more than 100 spectroscopically confirmed members. In the past years, our group has done a comprehensive multi-wavelength study of this galaxy cluster in-formation, finding different galaxy populations being overdense and indications for a filamentary super-protocluster with a size of 120 cMpc. I will focus on observations of the cold interstellar medium with radio and IR-facilities such as ALMA, ATCA and JWST for this structure which will have turned into one of the most massive galaxy clusters at our epoch. Especially, we will shed light on the growth of distant, star-forming galaxies in such an environment by examining the interplay between star formation, dust obscuration and the depletion of the molecular gas reservoir. These massive, heavily obscured sources are the likely progenitors of elliptical galaxies which dominate the light in local galaxy clusters. In addition, thought our census of the cold ISM of all members, we can constrain the molecular gas and star-formation rate density via various tracers (CO, dust, optical/NIR emission lines). Our multi-phase approach enables us to obtain a more and more complete picture of this archetypical protocluster and thus put constrains on its evolutionary stage and their members.