Map of the maximum signal-to-noise ratio (S/N) after cross-correlating the datacube with a 3D Gaussian template (see Sect. 5.2 for details on the construction of this image). Pixels with S/N_max <  4 and contaminating foreground sources are masked (regions in black). Thus, pixels shown in colour are a 2D projection of the 3D mask utilised to construct the adaptive narrow band image displayed in Fig. 5. The dashed contour demarcates region of connected pixels with S/N_max ≥ 6. This highlights that LAB 1, LAB 8 and the newly detected shell comprise a significantly detected contiguous region. The four enumerated features in this image are regions that contain pixels with S/N_max ≥ 6 that have no pixel connectivity at S/N_max ≥ 6 with the LAB1/LAB8 + shell structure; these detections are LAEs in the vicinity of the blob and are further discussed in Sect. 5.4. Previously known galaxies at z = 3.1 are indicated using the symbols in Fig. 1 and interesting features are annotated.