Oral Presentation

A proto-cluster of massive quiescent galaxies at z=4

Author(s): Masayuki Tanaka (NAOJ)

Presenter: Masayuki Tanaka (NAOJ)

We discuss an over-density region of several massive quiescent galaxies at z=4 in UDS. The over-density region is first identified using high-accuracy photometric redshifts based on deep multi-band photometry. Follow-up spectroscopic observations with MOSFIRE on Keck confirmed a massive quiescent galaxy at z=4. Using the spectrophotometric redshift technique (i.e., photometry + spectra), we confirm 4 additional quiescent galaxies at the same redshift. These quiescent galaxies are concentrated within 1 Mpc scale, and they form an early red sequence, suggesting that the red sequence appears during the initial phase of cluster formation. The over-density region exhibits a higher fraction of quiescent galaxies compared to the field. This is the first evidence for the Butcher-Oemler effect at such a high redshift. There are other recent studies that suggest that some of the massive quiescent galaxies at high redshifts are in locally dense environments, and we discuss implications of this trend in the context of quenching physics.