Southern part of Mon OB 1 east. The blue shaded patterns correspond to the regions where gravity is not dominant (case i), the red shaded patterns correspond to the candidate collapsing regions (case ii), and the yellow shaded patterns correspond to the candidate shock regions (case iii), overlaid on the ¹³CO integratedintensity grey scale map. Top row: based on the comparison between the velocity gradients, intensity gradients and the POS magnetic field direction derived from Planck: (a) based on ¹²CO data; (b) based on ¹³CO data. Bottom row: based on the comparison between the velocity channel gradients, intensity gradients and the POS magnetic field direction derived from Planck: (c) based on ¹²CO data; (d) based on ¹³CO data.