Relight the Candle: What happens to High Redshift Massive Quenched Galaxies

TL;DR

This study uses cosmological simulations to reproduce and analyze the properties and evolution of massive quenched galaxies at high redshift, revealing their formation, rejuvenation, and environmental characteristics.

Contribution

It demonstrates that such galaxies can be simulated with realistic properties and explores their evolutionary paths and environments in the cosmic web.

Findings

Simulated galaxies match observed stellar masses, sizes, and star formation histories.

Approximately 20% of these galaxies are accreted onto larger structures by z=2.

Most reside in side-nodes of Milky Way-sized halos, not in the most massive clusters.

Abstract

A puzzling population of extremely massive quiescent galaxies at redshifts beyond z=3 has recently been revealed by JWST and ALMA, some of them with stellar ages that show their quenching times to be as high as z=6, while their stellar masses are already above 5e10Msun. These extremely massive yet quenched galaxies challenge our understanding of galaxy formation at the earliest stages. Using the hydrodynamical cosmological simulation suite Magneticum Pathfinder, we show that such massive quenched galaxies at high redshifts can be successfully reproduced with similar number densities as observed. The stellar masses, sizes, formation redshifts, and star formation histories of the simulated quenched galaxies match those determined with JWST. Following these quenched galaxies at z=3.4 forward in time, we find 20% to be accreted onto a more massive structure by z=2, and from the remaining 80% about 30% rejuvenate up to z=2, another 30% stay quenched, and the remaining 40% rejuvenated on a very low level of star formation. Stars formed through rejuvenation are mostly formed on the outer regions of the galaxies, not in the centres. Furthermore, we demonstrate that the massive quenched galaxies do not reside in the most massive nodes of the cosmic web, but rather live in side-nodes of approximately Milky-Way halo mass. Even at z=0, only about 10% end up in small-mass galaxy clusters, while most of the quenched galaxies at z=3.4 end up in group-mass halos, with about 20% actually not even reaching 1e13Msun in halo mass.