Location of 16 SMGs extracted from our LABOCA map of the field of MRC1138 on top of the LABOCA signal-to-noise map. Blue squares represent spectroscopically confirmed membership to the protocluster structure at z ≈ 2.2. The blue star is the SCUBA source at z = 2.149, also detected in CO(1–0) by Emonts et al. (2013). Cyan pentagons show possible protocluster members. In the case of yellow circles, no reliable judgment on the cluster membership can be made. Red crosses are sources that can be securely excluded from the protocluster. The large circle has a diameter of ~240′′ (corresponding to a physical size 2 Mpc) and shows the region where all eight SMGs at z = 2.2 are located. The SMG overdensity is at least a factor four higher than compared to blank fields (Weiß et al. 2009) and not centered on the radio galaxy MRC1138 (DKB07). The spatial distribution of the SMG overdensity seems to be similar to the north-east and south-east filament-like structure traced by HAEs (plus symbols Kurk et al. 2004b; Koyama et al. 2013a) and in contrast to the location of passive quiescent galaxies clustered within 0.5 Mpc around the radio galaxy (red circles, filled if spectroscopically confirmed, see Tanaka et al. 2013). In addition, we show the fields of view of our Spitzer IRAC/MIPS, VLT FORS and Subaru MOIRCS datasets. North is at the top and east is to the left.