Oral Presentation
Clusters of Massive Quiescent Galaxies at z>2
Presenter: Tomokazu Kiyota (Kyoto University)
We report on the discovery of cluster candidates dominated by massive quiescent galaxies at z > 2. In the local universe, there is well-known galactic “segregation”, and galaxies are distributed according to their spectral type or morphology. However, the origin of this “segregation” is not fully understood yet. To address this problem, we focus on distant clusters of galaxies to identify the epoch when environmental effects started to play a role. The highest redshift clusters discovered so far are z ~ 2 and there are only a few of them. In this work, we aim to improve the statistics with a larger number of high redshift clusters as well as to explore higher redshifts. We use a deep multi-wavelength catalog based on the HSC-SSP and other public/collaborating surveys covering from the u-band to K-band (a.k.a. u2k catalog). We apply the photometric redshift technique to the catalog to infer redshifts of galaxies as well as their stellar masses and star formation rates. By measuring over-densities of massive galaxies in multiple redshift slices, we identify promising candidates of galaxy clusters at z >~ 2. Color-magnitude diagrams of galaxies around the candidates show a clear red sequence. We confirm that there is already a galactic “segregation” at z ~ 2; clusters show a higher fraction of quiescent galaxies than the field. We discuss implications of our results and conclude with future prospects.
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