Oral Presentation

Evolutionary Stages of Galaxy Cluster in the Distant Universe: Younger Galaxy Cluster Candidates at z~1.5

Author(s): Naoaki Yamamoto (Tohoku University), HSC^2 team

Presenter: Naoaki Yamamoto (Tohoku University)

In the local universe, physical properties of galaxies (e.g. color, age, star formation activity, morphology, etc.) strongly depend on their surrounding environment. For example, it is known that fraction of old, red, quiescent galaxies in galaxy clusters is high, while that of young, blue, star-forming galaxies in field is high. It is very important to understand when, where, and how this environmental dependence occurred in the past in order to unveil the history of galaxy formation and evolution. However, studies of environmental dependence in the distant universe have been limited due to small samples of galaxy clusters, and have been biased toward clusters with evolved evolutionary stages. Therefore, we conducted a large distant galaxy cluster survey using the Subaru HSC, which provided us with wider and deeper imaging data than the previous surveys. We used emission-line galaxies selected from narrow-band filters on the HSC to search for overdense regions of young star-forming galaxies at z~1.5. We discovered two extremely high dense regions of emission line galaxies (>8σ) in the COSMOS field. We investigated member galaxy properties using the latest COSMOS2020 catalog. Galaxy stellar mass functions of photo-z selected galaxies imply that one of them has a possibility to already host cluster scale halo. On the other hand, we cannot confirm clear environmental dependence of emission-line galaxies selected by the narrow-band filters in main sequence diagram, which is consitent with short quenching timescale scenario. Our results demonstrate potential power to reveal galaxy evolution in various environment. Finally, we plan to introuduce results in other fields except the COSMOS field at the same redshift range.