Lyα SB radial profiles extraction. Left: smoothed SB maps of the QSO sample (same as in Fig. 2) with the circular apertures used to extract radial profiles overlaid. The gray circle in each map indicates the 1 arcsec² region used for the QSO’s PSF normalization, which is neglected in our analysis. Right: extracted radial profiles inside each annulus. Open circles indicate negative values, shown here for completeness. The red line represents the 2σ SB limit rescaled to the area of each annulus. The dashed blue curve in the top panel is the best fit of the data points above the red line using an exponential function with the form SB_Lyα = Cexp( − r/r_h), where C = 85.3 ± 13.8 × 10⁻¹⁸ erg s⁻¹ cm⁻² arcsec⁻² and r_h = 11 ± 1 pkpc.