The Orion A molecular cloud complex as seen by the SCUBA-2 shared-risk observations. Left: continuum map at 850 μm in Jy per unit of 850 μm beam area. The blue contour traces the 20 K km s⁻¹ emission from the ¹²CO J = 3−2 molecular line. The labels identify the approximate location of different regions in the integral-shaped filament. Middle: continuum map at 450 μm map in Jy per unit of 450 μm beam area. The 60 submillimetre sources selected for this study (see Tables 1 and 2) are identified as follows: clumps are black plus symbols, protostars are red triangles and young stars with discs are green diamonds. Right: map of the spectral index α as defined in equation (3). Its relationship to the spectral index of emissivity β is given in equation (5). In the Rayleigh–Jeans approximation, this relation is simplified to β_RJ = α − 2. The red star identifies the position of θ Orionis C, the brightest member of the Trapezium cluster.