Upper left: signal-to-noise optimally extracted narrow-band image (Borisova et al. 2016) of the continuum-subtracted Lyα emission toward the AzTEC-3+LBG-3 system, rescaled to surface brightness units, and smoothed using a 2-pixel Gaussian kernel. The narrow band is built considering the 13 wavelength channels of the detection. The 5 white contours reveal the 1.3 to 3.8 erg s⁻¹ cm⁻² arcsec⁻² levels, which correspond to 3−10σ in this image. The black letters indicate the directions we refer to in the text (N = north, NW = northwest, S = south, SE = southeast, W = west of the SMG). The small black segment indicates the 1″ scale. We also show the continuum-subtracted Lyα surface brightness contours overplotted to the HST ACS F606W (upper right), F814W (lower left), and F160W (bottom right) images. The 0.5″-side square indicates the center of the F160W position of LBG-3. The PSF of our MUSE data is 0.7″, corresponding to about 4 kpc or 27 ckpc at z = 5.3. The eight red contours correspond to the [C II] emission (from 3σ to 10σ where 1σ = 2.38 × 10⁻⁴ Jy beam⁻¹) at 301.671−302.142 GHz, corresponding to −230 to 230 km s⁻¹ from the peak emission. The synthesized beam of the [C II] ALMA observations is 0.63″ × 0.56″ as reported in Riechers et al. (2014). The 3σ contour extends toward LBG-3.