How galaxies form in protoclusters

I will describe the cosmic star formation history of cluster galaxies using observations of clusters and protoclusters from z = 0 to 4. I will show that the star formation history of clusters differs from the global cosmic star formation history: cluster galaxies typically form their stars earlier and over a shorter period of time. I will use semi-analytic models of galaxy formation to explain why their star formation histories differ. I will show that the star formation density in protoclusters is extremely high due their high matter densities, but the simulations suggest there is no reversal in the star formation - density relation at high redshift. The differences in the star formation histories of field and cluster galaxies are caused by the gradual suppression of star formation, starting at z = 3, and getting stronger with time. The main mechanisms responsible for this suppression are tidal stripping and AGN feedback. Looking ahead, I will describe several testable predictions of the different evolutionary paths of cluster and field galaxies. Comparing these predictions with JWST observations of distant clusters and protoclusters can test our understanding of galaxy evolution.