Galaxy clusters and large structures in the Universe

Recent years have been rich in discoveries of our Universe, mapping galaxies and large structures, and determining theredshifts of millions of objects. Our local group is part of a supercluster of galaxies, Laniakea, which contains the Virgo galaxy cluster along with other clusters. Galaxy clusters are one of the tools we use to better constrain dark matter and the nature of dark energy. To this end, even more gigantic surveys are in preparation, with the Euclid satellite, but also on the ground with the LSST, for example. The various tools used are gravitational lenses, both strong and weak, the use of BAOs (Baryonic Acoustic Oscillations) as a standard rule, redshift-space distortions, and the growth rate of clusters over Hubble time. The study of clusters also makes it possible to determine the formation and evolution of galaxies, and their star formation rate, which is very depressed in clusters. More and more distant clusters can be detected, thanks to X-ray and millimetre Sunyaev-Zeldovich effects. Collisions between clusters are frequent, and traced by radio relics, remnants of relativistic electron populations originating from AGNs and re-accelerated by shocks. Numerical simulations of large-scale structure formation and cluster growth help to interpret the observations.