SILVERRUSH. VIII. Spectroscopic Identifications of Early Large-scale Structures with Protoclusters over 200 Mpc at z ∼ 6-7: Strong Associations of Dusty Star-forming Galaxies
Ono, Yoshiaki; Ouchi, Masami; Goto, Tomotsugu; Martin, Crystal L.; Smail, Ian; Fujimoto, Seiji; Harikane, Yuichi; Shibuya, Takatoshi; Inoue, Akio K.; Hashimoto, Takuya; Lee, Chien-Hsiu; Kohno, Kotaro; Clements, David L.; Im, Myungshin; Toft, Sune; Chapman, Scott; Hatsukade, Bunyo; Lin, Yen-Ting; Matsuoka, Yoshiki; Onodera, Masato; Nagao, Tohru; Wang, Wei-Hao; Lin, Lihwai; Kashikawa, Nobunari; Ao, Yiping; Umehata, Hideki; Lee, Minju M.; Overzier, Roderik; Kawaguchi, Toshihiro; Faisst, Andreas L.; Toshikawa, Jun; Jing, Yipeng; Marinello, Murilo; Donevski, Darko; Higuchi, Ryo
Japan, France, Italy, United States, Taiwan, Brazil, United Kingdom, China, Canada, South Korea, Denmark
Abstract
We have obtained three-dimensional maps of the universe in ∼200 × 200 × 80 comoving Mpc3 (cMpc3) volumes each at z = 5.7 and 6.6 based on a spectroscopic sample of 179 galaxies that achieves ≳80% completeness down to the Lyα luminosity of {log}({L}Lyα }/[{erg} {{{s}}}-1])=43.0, based on our Keck and Gemini observations and the literature. The maps reveal filamentary large-scale structures and two remarkable overdensities made out of at least 44 and 12 galaxies at z = 5.692 (z57OD) and z = 6.585 (z66OD), respectively, making z66OD the most distant overdensity spectroscopically confirmed to date, with >10 spectroscopically confirmed galaxies. We compare spatial distributions of submillimeter galaxies at z ≃ 4-6 with our z = 5.7 galaxies forming the large-scale structures, and detect a 99.97% signal of cross-correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust-unobscured galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars with star-formation rates (SFRs) ≳5 times higher than the main sequence, and particularly the SFR density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that are progenitors of the present-day clusters with halo masses of ∼1014 M ⊙.