a) Integrated intensity, , of N₂H⁺ (3–2) at 22′′ resolution with APEX and with a sampling rate of 10′′/pixel is shown in the upper panel. The positions of the SED-class sources of Fig. 1 are shown with their proper designations. b) Herschel map of the ρ Oph A core in the N₂H⁺ (6–5) line that is rotated to align with the APEX data. The (6–5) map has a resolution of 38′′ and is sampled at a rate of 16′′/pixel. Superposed, and shown as contours, is the map in the (3–2) line at degraded resolution. c) Orientation of the maps in the sky.