Optimally extracted SB maps of the Lyα nebulae surrounding the quasars (see Sect. 4.2). The white, gray, and black contours represent 2σ, 5σ, and 10σ, respectively. The values of σ are reported in Table 2. The green cross in the center represents the position of the quasar, determined by estimating the photocentroid of a channel map in a wavelength where the Lyα line is not present. North is up; east is left.