A dusty protocluster 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.; Young, A. J.
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Monthly Notices of the Royal Astronomical Society

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We report on deep SCUBA-2 observations at 850 $\mu$m 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. The SCUBA-2 observations detected, in addition to the binary system, 21 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.