S22A0007

This is a resubmission of our S21A program which was effectively completed only by 23% due to bad weather and instrument failure. The existence and age of massive (quiescent) galaxies at high redshifts will put strong constraints on galaxy formation theories, as there would be little cosmic time available for such matured systems to develop by the observed epoch. We will conduct this experiment at z∼5 for the first time using our unique, purpose-made medium-band filters K₁, K₂, and K₃ on SWIMS. As a pilot program, we aim to target 10 known proto-cluster candidates at z∼5 selected as highest over-densities (>4.9σ) of r-dropout LBGs in the HSC-SSP fields. By targeting those most overdense regions where galaxies are expected to form and grow earlier and faster in a biased manner, we can maximize the probability of our first discovery of at least a few massive monsters with M_*>6×10¹⁰M_⊙. We will be also able to quantify the bias/acceleration of galaxy formation in overdense regions in the early Universe. Those massive galaxy candidates will serve as excellent spectroscopic targets for ≥8–10m telescopes and JWST to characterize their properties such as accurate stellar masses and ages to put strong constraints on the initial onset of star formation beyond the reionization epoch.

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