PEGASUS (Pfs Emission-line GAlaxy SUrvey with Subaru): I. Three-dimensional large-scale structures at z > 1 probed with emission-line galaxies

To comprehensively understand the environmental effects on galaxy evolution, it is crucial to precisely map the distribution and thoroughly examine the properties of galaxies, including low-mass building blocks. Deep narrow-band imaging observations conducted with Hyper Suprime-Cam (HSC) on the Subaru Telescope systematically probed the distribution of low-mass star-forming galaxies as H α, [O II], and [O III] emission-line galaxies at 0.4 at most z at most1.6. We perform a comprehensive spectroscopic follow-up observation of these emission-line galaxies with narrow-band-based emission-line fluxes at least 2 times10-17 erg s-1 cm-2 within about1.8 deg squared area centered on the COSMOS field using `Ōnohi`ula - Prime Focus Spectrograph (PFS) on the Subaru Telescope. In this paper, we outline the data product and present the large-scale structures at z>1. 9079 out of 9917 of the targets are observed, and the redshifts of 92% of the observed targets are successfully confirmed. We survey groups, filamentary large-scale structures, and voids at z=1.19, 1.47, and 1.60 based on the three-dimensional distribution of 520-920 [O II] emission-line galaxies with stellar masses M at least10 9.5 M at each redshift. Groups with halo masses 1 times10 12-6 times10 13 M are identified along the filaments, whereas the most massive groups are located at the densest intersections of filaments as predicted by cosmological simulations. Voids hidden on the surface density maps are robustly extracted on the volume density map. Our spectroscopic sample provides a powerful basis for quantifying the evolution of galaxies along the diverse environments back in time toward cosmic noon epoch in forthcoming papers.