Views of the transverse velocity gradient across filament 8. Panel a: map of centroid velocities observed in ¹³ CO (2−1), shown from V_LSR = −1.86 km s ⁻¹ (blue) to V_LSR = +1.14 km s ⁻¹ (red). The crest of the filament is marked by a black line. The cores identified with getsources are shown by black ellipses, whose sizes correspond to the (major and minor) FWHM diameters of the equivalent Gaussian sources. Panel b: map of the linear transverse-velocity gradient model fitted on the blue-shifted eastern side (2.17 × X_offset km s⁻¹) and the red-shifted western side (0.74 × X_offset km s⁻¹) of the filament. Panel c: map of centroid velocities obtained after subtracting the transverse velocity gradient.