Overview of the G351 region. The left panel shows in color-scale the Spitzer 8 µm emission (Churchwell et al. 2009) and in contours the ATLASGAL 870 µm emission (Schuller et al. 2009). Contour levels start at the 4σ level of 240 mJy beam⁻¹. The middle and right panels present the molecular emission from the HCO⁺(1–0) and N₂H⁺(1–0) lines observed with the MALT90 survey (Jackson et al. 2013). In both cases, the colorscale shows the 1st moment maps (intensity-weighted peak velocities), and the contours present the integrated line emission or 0th moment from 5 to 95% of the respective peak emission. For N₂H⁺(1–0), the 1st moment map is from the isolated hyperfine component shifted by +8.0 km s⁻¹ to the v_lsr. Since the rms increases toward the map edges, we masked the emission outside the 5% 0th moment map for the N₂H⁺(1–0) map. The black and magenta boxes in the middle and right panels outline the areas shown in the following ALMA-IMF and ALMA central core images. Linear scale-bars are shown in the left and right panels, and the MALT90 beams are presented in the bottom corners.