Massive Galaxies are Larger in Dense Environments: Environmental Dependence of Mass-Size Relation of Early-Type Galaxies

TL;DR

This study reveals that massive early-type galaxies are significantly larger in dense environments, supporting hierarchical merger models and resolving previous observational inconsistencies.

Contribution

It provides the first observational evidence of environment-dependent size differences in massive early-type galaxies at low redshift.

Findings

Galaxies over $10^{11.2}M_{ m }$ are 20-40% larger in dense environments.

The environmental dependence holds for both BCGs and non-BCGs.

Results align with $$CDM simulations, indicating mergers influence galaxy growth.

Abstract

Under the $\Lambda$ cold dark matter ($\Lambda$CDM) cosmological models, massive galaxies are expected to be larger in denser environments through frequent hierarchical mergers with other galaxies. Yet, observational studies of low-redshift early-type galaxies have shown no such trend, standing as a puzzle to solve during the past decade. We analyzed 73,116 early-type galaxies at $0.1\leq z < 0.15$, adopting a robust nonparametric size measurement technique and extending the analysis to many massive galaxies. We find for the first time that local early-type galaxies heavier than $10^{11.2}M_{\odot}$ show a clear environmental dependence in mass-size relation, in such a way that galaxies are as much as 20-40% larger in densest environments than in underdense environments. Splitting the sample into the brightest cluster galaxies (BCGs) and non-BCGs does not affect the result. This result agrees with the $\Lambda$CDM cosmological simulations and suggests that mergers played a significant role in the growth of massive galaxies in dense environments as expected in theory.