LABOCA 870-μm image of the IRDC G304.74. The image is shown with linear scaling, and the colour bar indicates the flux density in units of Jy beam^-1. The rms level is 0.03 Jy beam^-1 (1σ). The first contour and the separation between contours is 3σ. The green plus signs show the submm peak positions, which were used as the line-observation target positions in the present study. The white circles indicate the nominal catalogue positions of the MSX 8-μm sources. The 1-pc scale bar and the effective LABOCA beam HPBW (~20″) are shown in the bottom left (modified from Paper I).