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Durham University

Department of Physics

Staff profile

Publication details for Professor Ian Smail

Chapman, S.C., Bertoldi, F., Smail, I., Blain, A.W., Geach, J.E., Gurwell, M., Ivison, R.J., Petitpas, G.R., Reddy, N. & Steidel, C.C. (2015). A blind CO detection of a distant red galaxy in the HS1700+64 protocluster. Monthly Notices of the Royal Astronomical Society: Letters 449(1): L68-L72.

Author(s) from Durham


We report the blind detection of 12CO emission from a distant red galaxy, HS1700.DRG55. We have used the IRAM Plateau de Bure Interferometer WideX, with its 3.6 GHz of instantaneous dual-polarization bandwidth, to target 12CO(3–2) from galaxies lying in the protocluster at z = 2.300 in the field HS1700+64. If indeed this line in DRG55 is 12CO(3–2), its detection at 104.9 GHz indicates zCO = 2.296. None of the other eight known z ∼ 2.30 protocluster galaxies lying within the primary beam (PB) are detected in 12CO, although the limits are ∼2 × worse towards the edge of the PB where several lie. The optical/near-IR magnitudes of DRG55 (RAB > 27, KAB = 22.3) mean that optical spectroscopic redshifts are difficult with 10-m-class telescopes, but near-IR redshifts would be feasible. The 24-μm-implied star formation rate (210 M⊙ yr−1), stellar mass (∼1011 M⊙) and 12CO line luminosity (3.6 × 1010 K km s−1 pc2) are comparable to other normal 12CO-detected star-forming galaxies in the literature, although the galaxy is some ∼2 mag (∼6 ×) fainter in the rest-frame UV than 12CO-detected galaxies at z > 2. The detection of DRG55 in 12CO complements three other 12CO detected UV-bright galaxies in this protocluster from previous studies, and suggests that many optically faint galaxies in the protocluster may host substantial molecular gas reservoirs, and a full blind census of 12CO in this overdense environment is warranted.