1.4 mm continuum emission, integrated intensities and mean velocities of the ¹³CO (2−1), C¹⁸O (2−1) and SO (5₆−4₅) lines in L1448-NB, L1448-C, NGC 1333-IRAS 2A, and L1527. Left panels: the 1.4 mm continuum emission. Other panels: the line mean velocities (first-order moment; background image), together with theline integrated intensities (zeroth-order moment; black contours). Contours are drawn at −3σ (dotted lines) 3σ, 6σ, 12σ and so on (solid lines). In each panel, the black crosses show the position of the main continuum peak(s). The blue and red lines in the left panels indicate the direction of the blue- and red-shifted lobes of the jet(s), respectively. The arrows in other panels indicate the direction of the velocity gradient, as determined from a linear fit of the mean velocity within 2″ of the continuum peak position. The gray sectors around each arrow show the 1σ uncertainty on the direction of the velocity gradient. The ellipse in each panel shows the synthesized beam. All coordinates are relative to the positions of the brightest continuum peak of each source (see Table 1).