LABOCA 870-μm (top), SABOCA 350-μm (middle), and a Spitzer IRAC/MIPS two-colour composite image (bottom; 4.5 μm in green and 24 μm in red) of the Class 0 protostellar core SMM 3 in Orion B9. The LABOCA and Spitzer images are shown with linear scaling, while the SABOCA image is shown with a square-root scaling to improve the contrast between bright and faint features. The LABOCA contours, plotted in white, go from 0.1 (~3.3σ) to 1.0 Jy beam^-1 in steps of 0.1 Jy beam^-1. The SABOCA contour levels, plotted in green, start at 3σ and are 0.18 Jy beam^-1 ×  [1,   2,   4,   6,   8,   10,   12,   14,   16] . In the bottom panel, the first SABOCA contour, i.e., the 3σ emission level, is plotted in white to guide the eye, and the white cross indicates the SABOCA peak position of SMM 3. The small subcondensations SMM 3b and 3c discovered in Paper III are labelled in the middle panel. The green plus sign shows the target position of our previous molecular-line observations (i.e., the submm peak position of the LABOCA map before adjusting the pointing; see Paper III for details). A scale bar indicating the 0.05 pc projected length is shown in the bottom left of the top panel, with the assumption of a 450 pc line-of-sight distance. The effective LABOCA and SABOCA beams,  ~20″ and , are shown in the lower right corners of the corresponding panels.