Galaxy populations in protoclusters at cosmic noon

Aims. We investigate the physical properties and redshift evolution of simulated galaxies residing in unvirialized cosmic structures (i.e., protoclusters) at cosmic noon, to understand the influence of the environment on galaxy formation. This work is intended to build clear expectations for the ongoing ODIN (One-hundred-deg2 DECam Imaging in Narrowbands) survey, which is mapping large-scale structures at z = 2.4,3.1, and 4.5 using Lyα-emitting galaxies (LAEs) as tracers. Methods. From the IllustrisTNG simulations, we define subregions centered on the most massive clusters ranked by total stellar mass at z = 0 and study the properties of galaxies within, including those of LAEs. To model the LAE population, we take a semi-analytical approach that assigns Lyα luminosity and equivalent width based on the UV luminosities to galaxies in a probabilistic manner. We investigate stellar mass, star formation rate (SFR), major merger events, and specific star formation rate of the population of star-forming galaxies and LAEs in the field- and protocluster environment and trace their evolution across cosmic time between z = 0−4. Results. We find that the overall shape of the UV luminosity function in simulated protocluster environments is characterized by a substantially shallower faint-end slope and a large excess on the bright end, signaling different formation histories for galaxies therein. The difference is milder for the Lyα luminosity function. While protocluster galaxies follow the same SFR-M★ scaling relation as average field galaxies, a larger fraction appears to have experienced major mergers in the last 200 Myr and as a result shows enhanced star formation at a ≈60% level, leading to a flatter distribution in both SFR and M★ relative to galaxies in the average field. We find that protocluster galaxies, including LAEs, begin to quench much earlier (z∼0.8−1.6) than field galaxies (z∼0.5−0.9); our result is in qualitative agreement with recent observational results and highlights the importance of large-scale environment on the overall formation history of galaxies.