Exposure map image for MUSE observations of LAB1 in the SSA22 field. The dashed rectangle indicates the zoomed-in region displayed in the spectral sequence shown in Fig. 3. Diagonal bands of lower exposure times are a result of masked out regions in the final cube stack due to contamination by bright satellite tracks or meteor trails in the individual exposures. To indicate the position and morphology of LAB 1 we also overlay the Lyα surface brightness contours from our MUSE adaptive narrow-band image (see Sect. 5.2).