tokens: represent the 1.3-mm (G09-83808, NGP-190387) and 3-mm (SGP-261206) continuum emission, at 5, 6, 7, 8, 9 × σ. Near-IR emission is seen clearly, coincident or near-coincident with the 1.3- or 3-mm continuum emission. At the depth of the VIKING observations (limiting magnitude, K AB ≃ 21.2), we do not expect to detect dust-obscured distant galaxies. The sources coincident with G09-83808 and SGP-261206 show, therefore, that these two DSFGs are amplified gravitationally by the foreground galaxies seen in the near-IR images. The galaxy in the foreground of SGP-83808 has z spec = 0.778, obtained using X-shooter on the VLT (Fig. 5 ), and is magnified by 8.2 ± 0.3, a factor determined using high-resolution ALMA continuum imaging (see Oteo et al., in preparation-a). The three galaxies revealed by the deeper Gemini imaging of NGP-190387 are considerably fainter, with K AB = 21.0, 22.3, 21.4, yet they are not coincident with the z = 4.42 DSFG and likely constitute a foreground lensing group. Towards G09-81106 we have detected two emission lines, CO(4–3) and CO(5–4), at 83.36 and 104.19 GHz (Fig. 3 ), both at z = 4.531. There is no suggestion of gravitational lensing for G09-81106, either via the presence of unusually bright near-IR galaxies in the field, or via its submm morphology as seen in high-resolution ALMA continuum imaging (Oteo et al., in preparation-a). Towards G09-83808 we have detected two faint emission lines, at 82.02 and 98.39 GHz (Fig. 3 ), corresponding to CO(5–4) and CO(6–5) at z = 6.026 ± 0.001 and 6.028 ± 0.001, respectively, so an average of 6.027 ± 0.001. These lines were also noted by Zavala et al. ( 2017 ) in a spectrum obtained using the Large Millimeter Telescope. G09-83808 is near-coincident with a foreground galaxy, seen clearly in near-IR imaging from the VIKING survey (see Fig. 4 – Edge et al. 2013 ), indicative of gravitationally lensing. This foreground galaxy has a spectroscopic redshift of 0.778, obtained using X-shooter on the 8-m Very Large Telescope (VLT; see Fig. 5 ). A lens model based on the morphology determined by high-resolution ALMA continuum imaging predicts a gravitational amplification of 8.2 ± 0.3 (Oteo et al., in preparation-a). Figure 5. Top: Spectrum of the lensing galaxy in the foreground of SGP-83808, as seen in the optical arm of VLT/X-shooter after integrating for 4 × 20 min on 2013 March 17. Below: The 1D spectrum, in grey, extracted using a simple box-car summation [090.A-0891(A), PI: Christensen]. To identify the lens redshift we binned these data heavily (see Modigliani et al. 2010 ; Christensen et al. 2012 ; Kausch et al. 2014 ), as illustrated in black, with the error spectrum shown in green, then fitted the redshift by χ 2 minimization using a 5-Gyr stellar population model (shown in red) from Bruzual Charlot ( 2003 ). We find z spec = 0.778 ± 0.006. Strong absorption features are labelled. The flux units are 10 −17 erg s −1 cm −2 Å −1 . For NGP-284357, we find at least two emission lines, at
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