Dense gas distribution within the ISF. Left: SCUBA-850 μm continuum emission (Johnstone & Bally 1999). Right: total N₂ H⁺ integrated intensity mosaic obtained by the combination of ALMA 12 m and IRAM 30m data. For reference, the positions of the Trapezium (white stars in OMC-1), the Orion BN source (yellow stars), the size of the Orion BN/KL explosion (green dashed circle; Bally et al. 2011), the 0.5 pc radius of the ONC (dashed line), the extension of the M43 nebula (dotted circle; Subrahmanyan et al. 2001) powered by NU Ori (isolated white star), and both Spitzer protostars (blue triangles; Megeath et al. 2012; Stutz et al. 2013; Furlan et al. 2016) plus continuum sources (blue crosses; Teixeira et al. 2016; Kainulainen et al. 2017; Palau et al. 2017) are shown in both panels. The corresponding beamsize (black solid dot) is indicated in the lower left corner in comparison with a characteristic 0.3 pc scale (black bar). The position of the zoom-in regions presented in Fig. 3 are enclosed by dashed boxes. A movie showing the combined ALMA 12 m plus IRAM 30m mosaic is available online.