ΛCDM predicts that the largest gravitationally bound overdensities in the initial density field collapse to form protoclusters, which gradually merge to form increasingly more massive clusters connected by filaments. This complex cosmic network is indeed observed in large galaxy redshift surveys.
At the same time very effective star formation quenching is observed in clusters at all redshifts, where the fraction of star forming galaxies is lower than in the field. Concomitantly the fraction of early type morphologies (lenticulars, ellipticals) is the highest.
We now know that this star formation suppression occurs at large distances from the cluster cores and that red galaxies are found preferentially close to the filament axes. A major thrust of ongoing research is to understand these transitions, namely to look for a possible threshold in density at which the shift in galaxy properties occur, to determine the origin of these transformations, and unveil their operating timescales.
In order to tackle these issues, we are engaged in large surveys at different redshifts (lookback times) in order to characterize the morphology of galaxies, the properties of their stellar population (age, metal content), but also the status of their gas reservoir, from which stars can form.