Discrepancies Between JWST Observations and Simulations of Quenched Massive Galaxies at $z > 3$: A Comparative Study With IllustrisTNG and ASTRID

TL;DR

This study compares JWST observations of massive quenched galaxies at high redshift with predictions from IllustrisTNG and ASTRID simulations, revealing significant underestimation of quenched galaxy abundance and highlighting the role of AGN feedback and environment in galaxy quenching.

Contribution

It demonstrates that current simulations underestimate the number of quenched massive galaxies at high redshift and emphasizes the need for improved AGN feedback models.

Findings

Simulations underestimate quenched galaxy abundance by up to 2 dex at z > 3.

AGN feedback is crucial for quenching in early massive galaxies.

Environmental effects influence quenching in lower-mass galaxies.

Abstract

Recent JWST observations have uncovered an unexpectedly large population of massive quiescent galaxies at $z>3$. Using the cosmological simulations IllustrisTNG and ASTRID, we identify analogous galaxies and investigate their abundance, formation, quenching mechanisms, and post-quenching evolution for stellar masses $9.5 < \log_{10}{(M_\star/{\rm M}_\odot)} < 12$. We apply three different quenching definitions and find that both simulations significantly underestimate the comoving number density of quenched massive galaxies at $z \gtrsim 3$ compared to JWST observations by up to $\sim 2$ dex. In both simulations, the high-$z$ quenched massive galaxies often host overmassive central black holes above the local $M_{BH}-M_\star$ relation, implying that AGN feedback is key in quenching galaxies in the early Universe. The typical quenching timescales for these galaxies are $\sim 200-600$ Myr. IllustrisTNG primarily employs AGN kinetic feedback, while ASTRID relies on AGN thermal feedback at $z > 2.3$, which is less effective and has a longer quenching timescale. Although these simulations differ in many aspects, making a direct comparison challenging, our findings suggest the need for improved physical models of AGN feedback in galaxy formation simulations. At lower stellar masses, the quenched galaxies have denser local environments than the star-forming galaxies, suggesting that environmental quenching helps quench less massive galaxies. We also study the post-quenching evolution of the high-$z$ massive quiescent galaxies and find that many experience subsequent reactivation of star formation, evolving into primary progenitors of $z=0$ brightest cluster galaxies.