The role of small-scale environments in the quenching of massive galaxies at 1<z<5

Massive quiescent galaxies (QGs) at high redshifts are likely progenitors of massive elliptical galaxies in the local Universe. Recent discoveries of high-redshift QGs in overdensities (galaxy groups and proto-clusters) have highlighted the relationship between massive galaxy quenching and their surrounding environment. We spectroscopically confirm a galaxy group associated with a massive QG at z spec=4.53 from the Lyman break feature using Subaru/FOCAS. This group consists of at least three star-forming galaxies within 150 pkpc of the QG, suggesting a physical association necessary for galaxy quenching. To investigate the role of the surrounding environment, we also perform a statistical analysis to characterize the typical environment of QGs at high redshifts. By selecting QGs using an SFR-based selection in the COSMOS field, we find that the quiescent fraction is higher in overdensities than in the field at 1<z<5. In particular, the elevated quiescent fraction within small-scale overdensities (about 200, pkpc) demonstrates that environmental quenching, possibly driven by galaxy mergers and interactions, plays a major role in the evolution of massive QGs at high redshifts. By extending the low-redshift mass and environmental quenching model up to z about 5, we confirm similar trends to those inferred from the SDSS red galaxy fraction at z<1. While environmental dependence weakens at z 3 for the overall population, a clear correlation persists specifically for more massive galaxies. This mass-dependent environmental effect suggests a downsizing trend, highlighting that the accelerated evolution of massive galaxies in high-density regions is already in place in the early Universe.