摘要：Most radiative transfer models assume that dust in spiral galaxies is distributed exponentially. In this paper our goal is to verify this assumption by analysing the two-dimensional large-scale distribution of dust in galaxies from the DustPedia sample. For this purpose, we have made use ofHerschelimaging in five bands, from 100 to 500μm, in which the cold dust constituent is primarily traced and makes up the bulk of the dust mass in spiral galaxies. For a subsample of 320 disc galaxies, we successfully performed a simultaneous fitting with a single Sérsic model of theHerschelimages in all five bands using the multi-band modelling codeGALFITM. We report that the Sérsic indexn, which characterises the shape of the Sérsic profile, lies systematically below 1 in allHerschelbands and is almost constant with wavelength. The average value at 250μm is 0.67 ± 0.37 (187 galaxies are fitted withn250 ≤ 0.75, 87 galaxies have 0.75 < n250 ≤ 1.25, and 46 – withn250 > 1.25). Most observed profiles exhibit a depletion in the inner region (atr < 0.3−0.4 of the optical radiusr25) and are more or less exponential in the outer part. We also find breaks in the dust emission profiles at longer distances (0.5−0.6) r25which are associated with the breaks in the optical and near-infrared. We assumed that the observed deficit of dust emission in the inner galaxy region is related to the depression in the radial profile of the HIsurface density in the same region because the atomic gas reaches high enough surface densities there to be transformed into molecular gas. If a galaxy has a triggered star formation in the inner region (for example, because of a strong bar instability, which transfers the gas inwards to the centre, or a pseudobulge formation), no depletion or even an excess of dust emission in the centre is observed.
