Demonstration of the covariance maps for the convolution of the −61 km s⁻¹ channel map (see Fig. 6) with rings of different radii. The first panel shows the channel map. The magenta circle emphasizes one of the obvious ring-like structures with a radius of 100″. The other five panels show the covariance maps from the convolution of rings with increasing radii. The radii are indicated at the same position in the map.