With increasing vLSR, the shell is displaced outwards, away from the centre of the bubble. This is the kinematic signature of an expanding half-shell. Each colour outlines the emission boundaries of channels 1 km s−1 wide from vLSR = 0 to vLSR = 7 km s−1. The origin (magenta star) corresponds to the position of θ1 Ori C (RA(J2000) = 5 h 35 min 16.46 s, dec.(J2000) = −5° 23′ 22.8″). In the velocity range 4–7 km s−1, [C ii] emission associated with OMC-4 starts to fill in the interior of the bubble. OMC-4 is a star-forming core near the front of the background molecular cloud and is not part of the Veil bubble.