Lyα nebula around J1259+0309. First panel: Optimally extracted Lyα nebula (zeroth moment) from continuum-subtracted MUSE data cube. The spatial projection of the segmentation mask is shown as a thick black contour around the detected emission, and it is approximately a 2.5σ = 2.45 × 10⁻¹⁸ erg s⁻¹ cm⁻² arcsec⁻² contour. Thin black contours enclose 5, 10 and 15σ regions. The black horizontal line indicates a scale of 10 pkpc. For reference, the PSF is depicted by a black circle with a diameter of 0.7″. Second panel: Velocity map of the emission with the zero point defined by z_sys. Third panel: Second moment map to show the equivalent Gaussian FWHM, where the instrumental FWHM_ins ≈ 170 km s⁻¹ has been subtracted in quadrature. Each image has a linear projected size of 14″ × 17″ and coordinates are relative to the quasar position. Last panel: Zoomed-in views of the inner region of the emission in four ≈290 km s⁻¹ wide velocity bins. The central value is indicated in the top-left corner of each image. Isophotal contours of SB values of 15, 30, and 45 × 10⁻¹⁸ erg s⁻¹ cm⁻² arcsec⁻² are shown.