Galaxy populations of ProtoClusters in cosmological hydrodynamical simulations

Abstract: The study of protoclusters at cosmic noon is essential to understand the impact on galaxies of the environment and of the transformational processes occurring in this epoch. This work tests the predictions of the DIANOGA cosmological hydrodynamical simulations of cluster progenitors at z=2.2, comparing them with observations, and investigates the environmental effects on galaxies by comparing protoclusters with an average volume of the Universe. We analyze 14 protoclusters and a cosmological box of 49 cMpc/h per side. We compare predictions and observations of the galaxy properties, including colors of galaxies obtained with radiative transfer, to analyze UVJ diagrams. We showed that the DIANOGA simulations produce a galaxy stellar mass function in broad agreement with observations, with a higher fraction of high-mass galaxies ($M_{\ast}>10^{10} \ M_{\odot}$) in massive halos in protoclusters, compared to the box. The same signal, with lower significance, is also observed in the wide-field protocluster structures, indicating an accelerated evolution of galaxies before their infall into massive halos. Our simulations underestimate SFRs of galaxies both in protoclusters and in the box, compared to observations, due to low gas reservoirs. We find a weak suppression of SFRs in protocluster galaxies (~0.05 dex), compared to the box, increasing up to ~0.25 dex in massive halos. The quenched galaxy fraction varies significantly across different protocluster halos, consistent with observations. The simulations show a strong dependence of quenched fractions on halo mass and an excess of quenched galaxies in the wide-field protocluster region, compared to the cosmological box. UVJ diagram analysis shows qualitative agreement with observed color distributions of star-forming and quenched galaxies, except for few massive galaxies with steeper reddening vectors than typically assumed in observations.