The beginning of the end for massive proto-cluster galaxies at z~2.

Understanding the build-up of stellar mass is one of the primary goals of extra-galactic astronomy. Various theoretical and observational studies find that star formation activity for galaxies in high density region peaks between redshift z=3-5, whereas for galaxies in the low density environment it peaks between redshift z=1-2. I will present the first measurements of formation histories of galaxies in a proto-cluster at z~2. We use Spectral Energy Distribution fitting module Prospector to measure the star formation histories. I will demonstrate how environment affects the stellar mass build-up in high stellar mass galaxies in our sample and how the relative star formation histories of galaxies at z=2 depends on their stellar masses. I will also present a comparison of star formation histories from Prospector to star formation histories from IllsutrisTNG cosmological simulations and discuss the role of mergers and their gas fractions in shaping the star formation histories of galaxies till z=2.