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

TL;DR

This study demonstrates that environmental factors at high redshift, especially local overdensity, significantly influence the stellar mass evolution of galaxies, improving predictive models of galaxy descendants at low redshift.

Contribution

It introduces a method to incorporate high-redshift environmental metrics into galaxy evolution models, highlighting the importance of local overdensity in predicting galaxy stellar mass at low redshift.

Findings

High-density environments lead to galaxies with up to eight times higher stellar mass at z~0.

Incorporating environmental metrics reduces prediction residuals by up to 35%.

Environmental factors become as important as stellar mass at z>2 in predicting galaxy evolution.

Abstract

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 $z\sim0$ 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 $z\sim3$ in determining the stellar mass of descendant galaxies at $z\sim0$. We identify the spherical overdensity within 1 cMpc ($\delta_{1,\mathrm{sp}}$) as the most important environmental predictor. Tracking galaxies at $z\sim3$ with similar initial stellar masses but different $\delta_{1,\mathrm{sp}}$ values, we find that, across all mass bins in both simulations, high-density environments produce $z\sim0$ descendants with median stellar masses up to eight times higher than the descendants of galaxies in low-density environments. For galaxies with $M_{*}\lesssim10^{10}M_{\odot}$, 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 $z\gtrsim2$, environmental factors become as important as stellar mass in predicting the stellar mass of $z\sim0$ descendants. Compared to using stellar mass at $z\sim3$ alone, incorporating $\delta_{1,\mathrm{sp}}$ reduces the scatter in the residuals between the predicted and actual stellar masses by approximately 20% in EAGLE and 35% in MAGNETICUM.