A blind CO detection of a distant red galaxy in the HS1700+64 protocluster

We report the blind detection of (CO)-C-12 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 (CO)-C-12(3-2) from galaxies lying in the protocluster at z = 2.300 in the field HS1700+64. If indeed this line in DRG55 is (CO)-C-12(3-2), its detection at 104.9 GHz indicates z(CO) = 2.296. None of the other eight known z similar to 2.30 protocluster galaxies lying within the primary beam (PB) are detected in (CO)-C-12, although the limits are similar to 2 x worse towards the edge of the PB where several lie. The optical/near-IR magnitudes of DRG55 (R-AB > 27, K-AB = 22.3) mean that optical spectroscopic redshifts are difficult with 10-m-class telescopes, but near-IR redshifts would be feasible. The 24-mu m-implied star formation rate (210 M-aS (TM) yr(-1)), stellar mass (similar to 10(11) M-aS (TM)) and (CO)-C-12 line luminosity (3.6 x 10(10) K km s(-1) pc(2)) are comparable to other normal (CO)-C-12-detected star-forming galaxies in the literature, although the galaxy is some similar to 2 mag (similar to 6 x) fainter in the rest-frame UV than (CO)-C-12-detected galaxies at z > 2. The detection of DRG55 in (CO)-C-12 complements three other (CO)-C-12 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 (CO)-C-12 in this overdense environment is warranted.