Velocity-integrated VLA ammonia contour maps obtained towards OMC-2 FIR 4, overlaid on the naturally weighted 2 mm-continuum map (grey scale). Contours for all the maps start at 3σ and increase by steps of 3σ. The 1σ rms values are 20 mJy beam^-1 km s^-1 for both NH₃(1, 1) and NH₃(2, 2). White crosses mark the positions of the three sources identified in this work (see Table 4).