Unveiling the properties and origin of massive quenched galaxies at $z\ge2$ in the COLIBRE hydrodynamical simulations

Abstract: JWST has uncovered a substantial population of Massive ($M_{\star} \gtrsim 10^{10 }\mathrm{M_{\odot}}$), Quenched Galaxies (MQGs) in the early Universe ($z \gtrsim 2$), whose properties challenge current galaxy formation models. In this paper, we examine this population of MQGs within the new COLIBRE cosmological hydrodynamical simulations. We report number densities and stellar mass functions in broad agreement with the latest observations. The predicted quenching and formation timescales are qualitatively consistent with observational inferences. Leveraging the state-of-the-art physics in COLIBRE, the model predicts that MQGs have dust and $\rm H_{2}$ fractions more than $1$ dex lower than their massive star-forming counterparts; while their sizes and kinematics remain broadly similar. We further explore the processes driving galaxies to become massive and quenched in COLIBRE, identifying active galactic nucleus (AGN) feedback as the primary quenching mechanism. Compared to star-forming galaxies of similar mass, MQGs host more massive black holes (BHs) and exhibit higher star formation efficiencies. These differences arise from their environments, particularly at local ($\rm 0.3\,cMpc$) to intermediate scales ($\rm 1.0\,cMpc$) before quenching, where overdense regions are associated with enhanced gas inflows, higher BH accretion and, hence, feedback power. We find that about $55\%$ of MQGs survive as the main progenitors of $z=0$ galaxies when they are selected at $z=3$, although up to $55\%$ experience rejuvenation episodes. Our results provide robust predictions for MQGs, show that tensions with observations are reduced when an effective observational uncertainty is forward-modelled, and clarify the mechanisms behind their origin.