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Fig. 3.


Lyα emission around the quasar pair in a field of view of about 200 kpc × 200 kpc (or 26″ × 26″). Left: “optimally extracted” Lyα surface brightness map obtained after subtraction of the quasars point-spread-function (PSF) and continuum in the MUSE datacube (details in Sect. 3.1). To highlight the significance of the detected emission, we indicate the contours for S/N = 3 and 4. This image reveals Lyα bridges extending between the quasar pair. Right: flux-weighted velocity-shift map with respect to the systemic redshift of QSO2 obtained from the first order moment of the flux distribution. A velocity gradient between QSO1 and the portion of the nebula southern than QSO2 is evident (Fig. 4). In both panels we indicate the position of the quasars QSO1 and QSO2 prior to PSF subtraction (white circles), and the masked interloper galaxy G, tentatively at z = 0.457 ± 0.001 (more details in Appendix B). Also, to guide the eye, we overlay a grid spaced by 10″ (or 77 kpc). We also highlight the location of a bright knot (white cross) whose SB value is relevant for the discussion in Sect. 5.1, the direction along which we trace the variations in SBLyα in Sect. 5.2.4, and the seeing circle for these observations (bottom left corner).

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