Velocity maps (colour scale, in km s^-1) of each line detected with PdBI towards OMC-2 FIR 4, with overlaying contours of the corresponding velocity-integrated maps. Contour levels are as in Fig. 3. The bottom-left ellipse in each panel represents the beam size. Crosses mark the phase centre of the observations, i.e. α(J2000) = 05^h35^m26.971^s, δ(J2000) = –05°09′56.77″.