A three-colour Spitzer image of SDC13 (24 μm in red, 8 μm in green and 3.6 μm in blue) overlayed with IRAM MAMBO 1.2 mm continuum contours (white) at 5, 15, 25, 35 and 45 mJy (left). The highlighted region (right) shows the two largest fragments (i.e. cores) in SDC13, MM1 and MM2, whose positions are marked with white crosses. Four sub-fragments are seen in the SMA 1.3 mm continuum observations of the region. The positions of these sub-fragments, A, B, C and D, are marked with yellow circles.