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

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 < ₁₀ (M_/{ M_) } < 12. We apply three different quenching definitions and find that both simulations significantly underestimate the comoving number density of quenched massive galaxies at z 3 compared to JWST observations by up to 2 dex. This fact highlights the necessity for improved physical models of AGN feedback in galaxy formation simulations. In both simulations, the high-z quenched massive galaxies often host overmassive central black holes above the standard M₁₇-M_ relation, implying that the AGN feedback plays a crucial role in quenching galaxies in the early Universe. The typical quenching timescales for these galaxies are 200-600 Myr. IllustrisTNG primarily employs AGN kinetic feedback, while ASTRID relies on AGN thermal feedback, which is less effective and has a longer quenching timescale. 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.