Optimally extracted narrow-band images of the Lyα emission mosaic_1548 (left panel) and contours in surface brightness units. The two white contours correspond to 3 and 4σ above the background, based on the S/N map provided by CubEx. In this case they correspond to 0.7 × 10⁻¹⁸ and 1.2 × 10⁻¹⁸ erg sec⁻¹ cm⁻² arcsec⁻². Stamps of the source in the HST F606W and F160W images are shown in the middle and right panels, together with the narrow-band surface brightness contours. The source within the contours of the right panel is COSMOS2015_841844 and it has a 0.4″ and a 1″ axes in the F160W image. The size of the pictures are adapted to contain exactly the entire emission.