HST, Lyα, and [C II] morphologies. (a). 10″ × 6″ cutout of the WFC3/F160W image in grayscale. The blue-filled contours represent {1,5,16,30} × 10⁻¹⁸ erg s⁻¹ cm⁻² arcsec⁻² levels of Lyα surface brightness based on the adaptive narrowband image described in the main text. The diameter of the blue circle represents the FWHM = $0\stackrel{″}{.}67$ of the PSF of the VLT/MUSE observations. The orange box outlines the $2\stackrel{″}{.}5\times 5^{″}$ zoom-in region displayed in the next panels. (b). ALMA Band 7 continuum image in logarithmic stretch. The white contours follow [C II] emission at {0.01,0.03,0.07,0.2,0.5} × Jy km s⁻¹, and highlight the non-detection of dust continuum in either CRISTAL-01a or the plume. (c). Adaptively masked [C II] velocity field (moment-1). A single colormap is assigned separately to the DSFG and CRISTAL-01a. The midpoint of the colormaps matches their corresponding systemic velocity, with the zero set at the redshift of the DSFG, z_[CII] = 4.5391. Again, overlaid contours show increasing levels of [C II] SB. The dashed line indicates the projected rotation axis at a $\mathrm{PA}=57\stackrel{°}{.}4$ through the [C II] kinematic center of the DSFG (see Appendix A). (d). Adaptively masked [C II] velocity dispersion map (moment-2), with [C II] SB contours.