Divergence maps of the column density gradients in N_H pix⁻¹ (left) and the velocity gradients in km s⁻¹ pix⁻¹ (middle) in the Horsehead nebula from the main-velocity layer from the ¹³CO (1–0) (top) and the C¹⁸O (1–0) (bottom) emission. Right: comparison maps of the sign between the velocity gradient divergence and the column density gradient divergence. The values –1 (blue) or 1 (red) show the pixels where velocity and column density gradients both converge or both diverge. The value 0 (gray) indicates regions where the sign of at least one gradient is ill-defined because its modulus is close to zero. The black lines show the filamentary structure and the diamond dots show the dense cores identified by the Herschel Gould Belt Survey (Könyves et al. 2020).