# Dark-ages Reionization and Galaxy Formation Simulation - XIII. AGN quenching of high-redshift star formation in ZF-COSMOS-20115

## TL;DR

This study uses a semi-analytic model to explore the formation and quenching of a massive quiescent galaxy at high redshift, highlighting the role of early mergers, black hole growth, and feedback in halting star formation.

## Contribution

It provides a detailed simulation-based explanation for the early quenching of a high-redshift massive galaxy, linking it to merger history and black hole activity.

## Key findings

- ZF-COSMOS-20115 likely hosted by a massive halo (~10^13 M_sun)
- Early mergers drove nuclear growth and quenched star formation
- Analogues were luminous quasars at z~5, possibly progenitors

## Abstract

Massive quiescent galaxies (MQGs) are thought to have formed stars rapidly at early times followed by a long period of quiescence. The recent discovery of a MQG, ZF-COSMOS-20115 at $z\sim4$, only 1.5 Gyr after the big bang, places new constraints on galaxy growth and the role of feedback in early star formation. Spectroscopic follow-up confirmed ZF-COSMOS-20115 as a MQG at $z=3.717$ with an estimated stellar mass of ${\sim}10^{11}\mathrm{M}_\odot$, showing no evidence of recent star formation. We use the Meraxes semi-analytic model to investigate how ZF-COSMOS-20115 analogues build stellar mass, and why they become quiescent. We identify three analogue galaxies with similar properties to ZF-COSMOS-20115. We find that ZF-COSMOS-20115 is likely hosted by a massive halo with virial mass of ${\sim}10^{13}\mathrm{M}_\odot$, having been through significant mergers at early times. These merger events drove intense growth of the nucleus, which later prevented cooling and quenched star formation. ZF-COSMOS-20115 likely remained quiescent at $z<3.7$. We find that the analogues host the most massive black holes in our simulation and were luminous quasars at $z\sim5$, indicating that ZF-COSMOS-20115 and other MQGs may be the descendants of high-redshift quasars. In addition, the model suggests that ZF-COSMOS-20115 formed in a region of intergalactic medium that was reionized early.