Anticorrelation between N₂H⁺ and C¹⁸O. Color background: N₂H⁺ (1–0) emission integrated over all seven hyperfine components. The noise in these maps is σ = (0.030, 0.027, 0.025, 0.029) Jy beam^-1 km s^-1 for IRAS4A, L1448C, L1157, and IRAS4B, respectively. The wedges show the N₂H⁺ intensity scale in Jy beam^-1 km s^-1. For the two lower panels the scaling is the same. Contours show emission of C¹⁸O (2–1) in steps of 6σ (IRAS4A) or 3σ (L1448C, L1157, and IRAS4B), starting at 3σ, with σ = (0.044, 0.029, 0.031, 0.033) Jy beam^-1 km s^-1 for IRAS4A, L1448C, L1157, and IRAS4B, respectively. The inlays in the upper right corners show the methanol emission as color background and contours in steps of 3σ, starting at 3σ inside the central 2′′, with σ = (0.028, 0.019, 0.027) Jy beam^-1 km s^-1 for IRAS4A, L1448C, and IRAS4B. In L1157, the methanol line has not been detected at a 3σ level. The filled ellipses in the lower left corner of the panels indicate the synthesized beam sizes of the N₂H⁺ observations at 3 mm. The dashed white lines illustrate the small-scale outflow directions (see Table 3 and Sect. 3.1), and the white crosses show the positions of the sources as listed in Table 1.