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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

  • Author(s): Harikane, Y
  • Ouchi, M
  • Ono, Y
  • Fujimoto, S
  • Donevski, D
  • Shibuya, T
  • Faisst, AL
  • Goto, T
  • Hatsukade, B
  • Kashikawa, N
  • Kohno, K
  • Hashimoto, T
  • Higuchi, R
  • Inoue, AK
  • Lin, YT
  • Martin, CL
  • Overzier, R
  • Smail, I
  • Toshikawa, J
  • Umehata, H
  • Ao, Y
  • Chapman, S
  • Clements, DL
  • Im, M
  • Jing, Y
  • Kawaguchi, T
  • Lee, CH
  • Lee, MM
  • Lin, L
  • Matsuoka, Y
  • Marinello, M
  • Nagao, T
  • Onodera, M
  • Toft, S
  • Wang, WH
  • et al.

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We have obtained three-dimensional maps of the universe in ∼200 × 200 × 80 comoving Mpc (cMpc ) 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, 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 ∼10 M 3 3 14 o˙

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