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


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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