Left: moment-zero map of HCG 16d. The white and black stars indicate the optical centres of HCG 16d and c, respectively, and the black ellipse shows the beam. A central depression is clearly visible around the white star marking the centre of HCG 16d. Right: first-moment contours for HCG 16d overlaid on the DECaLS grz image of HCG 16d and c. The central region of the galaxy is removed as the H I absorption feature would contaminate the first-moment map there. The green lines are separated by 20 km s⁻¹. While the velocity field is highly irregular, there is a slight gradient roughly aligned with the minor axis of the optical disc.