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

October 2019 • 2019ApJ...883..142H

Authors • Harikane, Yuichi • Ouchi, Masami • Ono, Yoshiaki • Fujimoto, Seiji • Donevski, Darko • Shibuya, Takatoshi • Faisst, Andreas L. • Goto, Tomotsugu • Hatsukade, Bunyo • Kashikawa, Nobunari • Kohno, Kotaro • Hashimoto, Takuya • Higuchi, Ryo • Inoue, Akio K. • Lin, Yen-Ting • Martin, Crystal L. • Overzier, Roderik • Smail, Ian • Toshikawa, Jun • Umehata, Hideki • Ao, Yiping • Chapman, Scott • Clements, David L. • Im, Myungshin • Jing, Yipeng • Kawaguchi, Toshihiro • Lee, Chien-Hsiu • Lee, Minju M. • Lin, Lihwai • Matsuoka, Yoshiki • Marinello, Murilo • Nagao, Tohru • Onodera, Masato • Toft, Sune • Wang, Wei-Hao

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 .


IPAC Authors


Andreas Faisst

Assistant Scientist