# Massive Quiescent Galaxies at z>3 in The Millennium Simulation Populated by A Semi-analytic Galaxy Formation Model

## TL;DR

This study uses the Millennium simulation with a semi-analytic model to show that massive quiescent galaxies observed at high redshift can naturally form within current galaxy formation theories, highlighting the role of AGN feedback.

## Contribution

It demonstrates that current semi-analytic models can reproduce high-redshift quiescent galaxies, including the specific case of ZF-COSMOS-20115, and assesses their rarity and formation mechanisms.

## Key findings

- High-redshift quiescent galaxies are rare (~2%) but can form naturally in models.
- The AGN feedback mechanism successfully explains the quenching of star formation at z>3.
- Multiple analogues of ZF are found at z~3.6 in the simulation volume.

## Abstract

We take advantage of the statistical power of the large-volume dark-matter-only Millennium simulation, combined with a sophisticated semi-analytic galaxy formation model, to explore whether the recently reported $z=3.7$ quiescent galaxy ZF-COSMOS-20115 (ZF; Glazebrook et al. 2017) can be accommodated in current galaxy formation models. In our model, a population of quiescent galaxies (QGs) with stellar masses and star formation rates comparable to those of ZF naturally emerges at redshifts $z<4$. There are two and five ZF analogues at the redshift $3.86$ and $3.58$ in the Millennium simulation volume, respectively. We demonstrate that, while the $z>3.5$ massive QGs are rare (about 2\% of the galaxies with the similar stellar masses), the existing AGN feedback model implemented in the semi-analytic galaxy formation model can successfully explain the formation of the high-redshift QGs as it does on their lower redshift counterparts.