The influence of external environment at cosmic noon on the subsequent evolution of galaxy stellar mass

Connecting high-redshift galaxies to their low-redshift descendants is one of the most important and challenging tasks of galaxy evolution studies. In this work, we investigate whether incorporating high-redshift environmental factors improves the accuracy of matching high-redshift galaxies to their z ∼ 0 descendants, using data from the Eagle and Magneticum simulations. Using random forest regression, we evaluate the relative importance of a set of environmental metrics at z ∼ 3 in determining the stellar mass of descendant galaxies at z ∼ 0. We identify the spherical overdensity within 1 cMpc (δ1, sp) as the most important environmental predictor. Tracking galaxies at z ∼ 3 with similar initial stellar masses but different δ1, sp values, we find that, across all mass bins in both simulations, high-density environments produce z ∼ 0 descendants with median stellar masses up to eight times higher than the descendants of galaxies in low-density environments. For galaxies with M* ≲ 1010M⊙, the difference is attributable to more merger-induced mass growth in high-density environments, whereas for higher-mass galaxies, it results from a combination of enhanced in-situ star formation and greater external mass accretion. By assessing the importance of overdensity across multiple scales and redshifts, we find that at z ≳ 2, environmental factors become as important as stellar mass in predicting the stellar mass of z ∼ 0 descendants. Compared to using stellar mass at z ∼ 3 alone, incorporating δ1, sp reduces the scatter in the residuals between the predicted and actual stellar masses by approximately 20% in Eagle and 35% in Magneticum.