Same as Fig. 1, but for NGC 2024 in Orion B. The H₂ column density map of the Orion B region is from HGBS data (Könyves et al., in prep.; see also Schneider et al. 2013). The angular resolutions of HCN, HCO⁺, and H¹³CO⁺, and H¹³CN maps are 30″, 30″, 30″, and 40″. The white contour in panel a and magenta dashed contours in panels e and f indicate the A_V = 8 level derived from the Herschel column density map smoothed to 30″ resolution. In panels e and f, the magenta solid contour indicates the rough A_V column density level above which significant line emission is detected, i.e., A_V = 20 for H¹³CN (1–0) and A_V = 16 for H¹³CO⁺ (1–0).