A dusty proto-cluster surrounding the binary galaxy HerBS-70 at z = 2.3

Bakx, Tom J L C; Berta, S; Dannerbauer, H; Cox, P; Butler, K M; Hagimoto, M; Hughes, D H; Riechers, D A; van der Werf, P P; Yang, C; Baker, A J; Beelen, A; Bendo, G J; Borsato, E; Buat, V; Cooray, A R; Dunne, L; Dye, S; Eales, S; Gavazzi, R; Harris, A I; Ismail, D; Ivison, R J; Jones, B; Krips, M; Lehnert, M D; Marchetti, L; Messias, H; Negrello, M; Neri, R; Omont, A; Perez-Fournon, I; Nanni, A; Chartab, N; Serjeant, S; Stanley, F; Tamura, Y; Urquhart, S A; Vlahakis, C; Weiß, A and Young, A J (2024). A dusty proto-cluster surrounding the binary galaxy HerBS-70 at z = 2.3. Monthly Notices of the Royal Astronomical Society, 530(4)

DOI: https://doi.org/10.1093/mnras/stae1155

Abstract

We report on deep SCUBA-2 observations at 850 μm and NOrthern Extended Millimetre Array (NOEMA) spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive (M_* ≈ 2 × 10¹¹ M_⊙) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at z = 2.3, with the East component (HerBS-70E) hosting an Active Galactic Nucleus (AGN). The SCUBA-2 observations detected, in addition to the binary system, twenty-one sources at >3.5σ over an area of ∼25 square comoving Mpc with a sensitivity of 1σ₈₅₀ = 0.75 mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4–3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times (80 − 500 Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around 5 × 10¹³ M_⊙, with a projected current-day mass of 10¹⁵ M_⊙, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.

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