First redshift determination of an optically/ultraviolet faint submillimeter galaxy using CO emission lines

We report the redshift of a distant, highly obscured submillimeter galaxy (SMG), based entirely on the detection of its CO line emission. We have used the newly commissioned Eight MIxer Receiver at the IRAM 30 m telescope, with its 8 GHz of instantaneous dual-polarization bandwidth, to search the 3 mm atmospheric window for CO emission from SMM J14009+0252, a bright SMG detected in SCUBA Lens Survey. A detection of the CO(3-2) line in the 3 mm window was confirmed via observations of CO(5-4) in the 2 mm window. Both lines constrain the redshift of SMM J14009+0252 to z = 2.9344, with high precision (δz = 2 × 10-4). Such observations will become routine in determining redshifts in the era of ALMA