Oral Presentation
Ruby-Rush: The quest of red monsters lurking in the protoclusters at z~5.
Presenter: Kosuke Takahashi (Tohoku University)
Understanding when and where massive galaxies formed and when and how they quenched star-forming activity is critical to the theory of galaxy formation. It can also put strong constraints on the efficiency of galaxy formation in the early universe and, by extension, on the current standard theory of hierarchical structure formation. Although Milky Way-class (10^11M⊙) galaxies have already been confirmed at z~4, we aim to go further back in time and search for protoclusters at z~5 to discover mature, massive galaxies of comparable mass that have almost quenched star formation activity.
To search for such galaxies, we are conducting the Ruby-Rush project (PI: Kodama), which targets the primordial cluster candidate regions where many Lyman break galaxies are hosted, as found by the Gold-Rush project (Toshikawa et al. 2018). Using the near-infrared instrument SWIMS on the Subaru Telescope, we have successfully discovered massive quiescent galaxy candidates at z∼5 by neatly bracketing the Balmer break feature, which is prominent in the spectra of galaxies that have quenched star formation activity, with two medium-band filters (K2 and K3). To remove contaminant galaxies with strong emission lines in the K3 filter and also foreground dusty red galaxies, we perform SED fitting by combining HSC (optical) and IRAC (~4μm) data. As a result, we have successfully identified several robust candidates. In this talk, we will report these new findings and early results on the properties of the candidate galaxies, their spatial distribution, and comparison in spatial distribution with Lyman-Break galaxies, and discuss the accelerated massive galaxy formation in the high density regions only a billion years after the Big Bang.
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