Left panel: χ² map in the z-T_d plane, where z and T_d are the redshift and the dust temperature assumed for the 870 μm source detected with LABOCA. The two 870 μm peaks shown in Fig. 2 and the two low-z sources (at z = 0.6 and 0.3) shown in Fig. 1 are fitted simultaneously at all wavelengths from 100 to 870 μm assuming a modified black-body SED for each source (7 free parameters). The white contours show the 1σ, 2σ, 3σ, and 4σ confidence levels. Middle and right panels: best-fit FIR luminosity in log without any lensing correction in the z-T_d plane for the two 870 μm peaks. The white contours are spaced by 0.5 dex. The χ² 3σ confidence level is overplotted in red.