Distribution of T and β values estimated with IRIS 100 μm data and Planck data at frequencies 353 GHz and higher. The values have been calculated pixel-by-pixel using maps at a resolution of 5′. Left frame contains all pixels inside the coverage of SPIRE maps. Right frame contains from each field only 25% of the pixels with the highest column densities (fourth quartile). The column densities have been estimated using the same data and a fixed value of spectral index, β = 1.8.