Correlation coefficient of the residual emission with the 857GHz residual. Similar to Fig. 16, the solid line here is the normalised modified black body SED fit using 3000, 545 and 353GHz data. We assumed a fixed β = 1.8, except for the six most diffuse fields (MC, G86, AG, N1, SP and BOOTES) where the residual emission is dominated by the CIB fluctuations. In these fields β = 1.8, typical of diffuse Galactic dust emission, does not provide a good fit; these SEDs require a smaller value of β (see text).