Cake Talk by Takumi Kakimoto
Massive quiescent galaxies at z~4 are likely progenitors of massive elliptical galaxies in the local Universe. They have been the subject of many recent papers to constrain the physical drivers to stop their star formation activities (quenching). To date, only a few massive quiescent galaxies at z~4 are spectroscopically confirmed, and the detailed physics of their quenching mechanisms is still unclear. Recently, we reported on the spectroscopic confirmation of a massive quiescent galaxy (QG) at z=4.53 in the COSMOS field (Kakimoto et al. 2024). This galaxy is among the youngest QGs confirmed so far with a formation redshift of 5.2 (200 Myr old). A unique aspect of the galaxy is that it is in an extremely dense region, suggesting that effects from surrounding environment are important to quench the galaxy. To extend this work, we make an attempt to unveil the typical environment of massive QGs at high redshifts. By selecting QGs at z>1 using high-accuracy photometric redshifts in the COSMOS field, we find that the ratio of QGs is higher in group-like environment. We summarize differences between isolated QGs and those in group environment and discuss their implications for the quenching physics.