Left: HST F390W band thumbnail image of Ion3, size 5″ × 5″. Three zoom-in cut outs of sizes 1.5″ × 1.5″ are shown on the right side and F390W, F814W, and F140W bands with their expected PSFs in the upper left corner, blue circle. The HST F390W band probes LyC flux from 890 Å and blueward (note: the F390W band misses the first ∼20 Å of LyC flux). Green arrows point toward two clumpy structures (A and B) at z = 3.999 where LyC flux is detected. The third clumpy structure, pointed to with a purple arrow (C), very close to the LyC leaking sources, is most likely a low-z interloper, which is masked before the LyC flux is measured. Finally, the blue circle is adopted as the aperture to measure LyC flux, with a diameter of 0.36″, while the cyan rectangle (D) encloses the source that probably contaminates the LyC flux detected from the FORS spectroscopy. The blue lines indicate the VLT FORS slit position, showing that source D enters the slit and likely contaminates the LyC flux detected in FORS spectroscopy. The grey lines show the VLT X-Shooter slit position. The second observed band is F814W and covers non-ionizing UV flux, where both LyC leaking clumps are detected. The third panel is the F140W band, where Ion3 is detected as a single bright blob, which is not resolved due to the lower spatial resolution of WFC3/IR. The three small green diamonds are centered on the clumpy sources A, B, and C in the F390W image, with their corresponding positions also shown in the F814W and F140W images. It is noticeable that clump A detected in F390W is slightly offset from clump A observed in F814W.