Cake Talk by Kei Ito from The University of Tokyo
Recent multi-band observations have found that galaxies with suppressed star formation activity exist even in the high redshift universe. The state-of-art spectrograph has now confirmed them up to z~4. On the other hand, it is not well understood why they get quenched at such a high redshift and where they live. Here, I will introduce our two recent works for quiescent galaxies in the COSMOS field, (1) X-ray (Chandra) and radio (VLA) stacking analysis to explore their AGN activity and its connection to quenching and (2) the discovery of an overdense structure of quiescent galaxies at z=2.77 which are likely to be a new type of protocluster with the Keck/MOSFIRE observation.