Centre of the three sub-regions of the mapped area showing the best-fit models (green) for the observed (blue) N₂H⁺ (3–2) and (6–5) line profiles (left and right, respectively). The radiative transfer with ALI takes the overlapping transitions of the 38 hyperfine components into account, with the frequencies of Pagani et al. (2009). In the small frames, the numbers in the upper left corners are equatorial offsets in arcsec from the map origin (0, 0). In the lower left frames, the scales are given for T_mb (K) and Δv = υ−υ_LSR (υ_LSR = +3.5 km s^-1), respectively (Figs. 5 and 6).