The role of AGN feedback in forming early massive quenched galaxies in COLIBRE

JWST has revealed a substantial population of massive (M★≳10^10M⊙) quenched galaxies (MQGs) at z≳2, whose short quenching timescales strongly suggest that active galactic nucleus (AGN) feedback is the dominant quenching mechanism. In this talk, we use the new COLIBRE cosmological hydrodynamical simulations to investigate how AGN feedback drives the formation and evolution of MQGs. Our fiducial COLIBRE simulation, which adopts a single thermal AGN feedback model, reproduces the observed MQG number densities and stellar mass functions in broad agreement with JWST constraints. In contrast, simulations employing a hybrid AGN feedback model, combining thermal and kinetic (BH-spin-regulated jet) modes, produce significantly lower MQG number densities at high redshift, due to less efficient early black hole (BH) growth. Despite these differences, AGN feedback remains the dominant quenching mechanism in early MQGs across all models. Compared to massive star-forming galaxies, MQGs host more massive BHs and experience enhanced BH accretion prior to quenching, leading to more efficient energy injection into the surrounding gas, driven by their overdense environments. Consequently, MQGs exhibit dust and molecular gas fractions more than an order of magnitude lower than their star-forming counterparts, while retaining similar sizes and kinematics. Finally, we find that ∼55% of MQGs undergo rejuvenation episodes, highlighting the often temporary impact of AGN feedback at high redshift.