Left: Spitzer 24 μm image of SDC13 (greyscale) on which we over-plotted the MAMBO 3 mJy/beam contour (yellow). In this image we also report the positions of the seven protostellar sources identified along the SDC13 filaments (purple circles), along with the detection of two extra sources located on the edge of the outer edge of the contour (blue circles). Right: 8 μm image of SDC13 (greyscale). The contour is the same as in the left panel. The purple circles mark the positions of the nine 8 μm sources identified towards the identified 24 μm sources. The meaning of the symbol’s colour is the same as in the left panel.