HST imaging of the field in the F814W filter, single orbit (Scoville et al. 2007). The image is smoothed with a Gaussian with the same FWHM as the PSF (0.1″) to enhance visibility of faint features; the color bar shows relative pixel fluxes. Green contours show the Lyα emission. Blue circles are Lyα emitters identified inside the nebula from the KCWI data (within 2000 km s⁻¹): the small offsets with respect to the HST positions are a combined effect of the noise in the Lyα cube affecting their recovery and the accuracy of the astrometric solution of the KCWI cube. Cyan circles mark two galaxies in the structure identified from UV absorption, and red circles show the positions of the ALMA galaxy detections.