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Article, 2024

DEIMOS spectroscopy of z=6 protocluster candidate in COSMOS - a massive protocluster embedded in a large-scale structure?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, ISSN 0035-8711, 0035-8711, Volume 527, 3, Pages 6591-6615, 10.1093/mnras/stad3409

Contributors

Brinch, Malte (Corresponding author) [1] [2] Greve, Thomas R. [1] [2] [3] [4] Sanders, David B. [5] McPartland, Conor J. R. [1] [5] [6] [7] [8] [9] Chartab, Nima [10] Gillman, Steven [1] [2] Vijayan, Aswin P. [1] [2] Lee, Minju M. [1] [2] Brammer, Gabriel [1] [8] [9] Casey, Caitlin M. [11] [12] Ilbert, Olivier [13] [14] Jin, Shuowen [1] [2] Magdis, Georgios [1] [2] [8] [9] [15] McCracken, H. J. [14] [16] [17] Sillassen, Nikolaj B. [1] [2] Toft, Sune [1] [8] [9] [18] [19] Zavala, Jorge A.

Affiliations

[1] Cosm Dawn Ctr DAWN, Copenhagen, Denmark

[NORA names:

KU University of Copenhagen

[2] Tech Univ Denmark, Natl Space Inst, DTU Space, Elektrovej 327, DK-2800 Lyngby, Denmark

[NORA names:

DTU Technical University of Denmark

[3] UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England

[NORA names:

[4] UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England

[NORA names:

[5] Univ Hawaii, Inst Astron, 2680 Woodlawn Dr, Honolulu, HI 96822 USA

[NORA names:

(... more)

[6] Univ Calif Riverside, Dept Phys & Astron, 900 Univ Ave, Riverside, CA 92521 USA

[NORA names: United States; America, North; OECD];

[7] Univ Calif Riverside, Dept Phys & Astron, 900 Univ Ave, Riverside, CA 92521 USA

[NORA names: United States; America, North; OECD];

[8] Univ Copenhagen, Niels Bohr Inst, Jagtvej 128, DK-2200 Copenhagen, Denmark

[NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD];

[9] Univ Copenhagen, Niels Bohr Inst, Jagtvej 128, DK-2200 Copenhagen, Denmark

[NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD];

[10] Carnegie Inst Sci, Observ, 813 Santa Barbara St, Pasadena, CA 91101 USA

[NORA names: United States; America, North; OECD];

[11] Univ Texas Austin, Dept Astron, 2515 Speedway Blvd Stop C1400, Austin, TX 78712 USA

[NORA names: United States; America, North; OECD];

[12] Univ Texas Austin, Dept Astron, 2515 Speedway Blvd Stop C1400, Austin, TX 78712 USA

[NORA names: United States; America, North; OECD];

[13] Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France

[NORA names: France; Europe, EU; OECD];

[14] Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France

[NORA names: France; Europe, EU; OECD];

[15] Natl Observ Athens, Inst Astron Astrophys Space Applicat & Remote Sen, GR-15236 Athens, Greece

[NORA names: Greece; Europe, EU; OECD];

[16] CNRS, UMR 7095, Inst Astrophys Paris, 98 Bis Blvd Arago, F-75014 Paris, France

[NORA names: France; Europe, EU; OECD];

[17] CNRS, UMR 7095, Inst Astrophys Paris, 98 Bis Blvd Arago, F-75014 Paris, France

[NORA names: France; Europe, EU; OECD];

[18] Natl Astron Observ Japan, 2 21 1 Osawa, Mitaka, Tokyo 1818588, Japan

[NORA names: Japan; Asia, East; OECD];

[19] Natl Astron Observ Japan, 2 21 1 Osawa, Mitaka, Tokyo 1818588, Japan

[NORA names: Japan; Asia, East; OECD]

Abstract

We present the results of our Keck/DEep Imaging Multi-Object Spectrograph spectroscopic follow-up of candidate galaxies of I-band-dropout protocluster candidate galaxies at z similar to 6 in the COSMOS field. We securely detect Lyman alpha emission lines in 14 of the 30 objects targeted, 10 of them being at z = 6 with a signal-to-noise ratio of 5-20; the remaining galaxies are either non-detections or interlopers with redshift too different from z = 6 to be part of the protocluster. The 10 galaxies at z approximate to 6 make the protocluster one of the riches at z > 5. The emission lines exhibit asymmetric profiles with high skewness values ranging from 2.87 to 31.75, with a median of 7.37. This asymmetry is consistent with them being Ly alpha, resulting in a redshift range of z = 5.85-6.08. Using the spectroscopic redshifts, we recalculate the overdensity map for the COSMOS field and find the galaxies to be in a significant overdensity at the 4 sigma level, with a peak overdensity of delta = 11.8 (compared to the previous value of delta = 9.2). The protocluster galaxies have stellar masses derived from BAGPIPES spectral energy distribution fits of 10(8.29)-10(10.28) M-circle dot and star formation rates of 2-39 M-circle dot yr(-1), placing them on the main sequence at this epoch. Using a stellar-to-halo-mass relationship, we estimate the dark matter halo mass of the most massive halo in the protocluster to be similar to 10(12) M-circle dot. By comparison with halo mass evolution tracks from simulations, the protocluster is expected to evolve into a Virgo- or Coma-like cluster in the present day.

Keywords

(cosmology:) large-scale structure of Universe, galaxies: evolution, galaxies: high-redshift

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