(a) Dust temperature map of the Sgr B2 molecular cloud. (b) Optical depth image at 250 μm. (c) Map of the dust emissivity index, β (see Eq. (2)). The size of the beam (FWHM = 36.9″) is plotted at the down-right side of the images. The size of the images is  ~7.0  ×  8.22 arcmin², equivalent to  ~17.3  ×  20.3 pc². White numbers on the optical depth image represent the nine positions, whose SED and fitting are shown in Fig. 8.