Explaining ultra-massive quiescent galaxies at $3 < z < 5$ in the context of their environments

TL;DR

This paper demonstrates that the early formation of ultra-massive quiescent galaxies at high redshifts can be explained by their residing in significant overdensities, using an environment-aware statistical model.

Contribution

The authors develop a modified Extreme Value Statistics code that incorporates galaxy clustering to better understand the formation of massive galaxies in dense environments.

Findings

Ultra-massive quiescent galaxies are found in significant overdensities.

Environment-aware modeling reduces tension with simple galaxy formation models.

Clustering plays a key role in early galaxy assembly.

Abstract

The swift assembly of the earliest galaxies poses a significant challenge to our understanding of galaxy formation. Ultra-massive quiescent galaxies at intermediate redshifts ($3 < z < 5$) currently present one of the most pressing problems for theoretical modeling, since very few mechanisms can be invoked to explain how such galaxies formed so early in the history of the Universe. Here, we exploit the fact that these galaxies all reside within significant overdensities to explain their masses. To this end, we construct and release a modified version of the Extreme Value Statistics (EVS) code which takes into account galaxy environment by incorporating clustering in the calculation. With this new version of EVS, we find that ultra-massive quiescent galaxies at $3<z<5$ do not present as serious a tension with simple models of galaxy formation when the analysis of a given galaxy is conditioned on its environment.