Clusters are the latest systems to form, and therefore they are most likely to reveal evidence for recent evolution. This study will observe in neutral hydrogen two clusters at the lowest redshift where signs for cosmological evolution have been found (z=0.2). A complementary study of the nearest cluster of galaxies, the Virgo cluster, will also be continued. These studies will help our understanding of the physical mechanisms that drive the evolution of individual galaxies. The main tool is a powerful new backend at the Westerbork Synthesis Radio Telescope, which enables probing a huge volume around these clusters, plus optical and X-ray data. A pilot study has been awarded time, and the observations have started. The science goals will focus on the evolution of the cold gas that has been brought into the hot intergalactic medium, such as the large-scale structure in the gas properties and how the gas reservoirs get affected as the galaxies come close to the cluster. The Virgo project is a legacy project and the Principal Investigator has made a public web page where all results are available.
