Dust emission profiles of DustPedia galaxies ? ??

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 of Herschel imaging in five bands, from 100 to 500 μ m, 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 the Herschel images in all five bands using the multi-band modelling code GALFITM . We report that the Sérsic index n , which characterises the shape of the Sérsic profile, lies systematically below 1 in all Herschel bands and is almost constant with wavelength. The average value at 250 μ m is 0.67?±?0.37 (187 galaxies are fitted with n ~(250)?≤?0.75, 87 galaxies have 0.75? ?1.25). Most observed profiles exhibit a depletion in the inner region (at r ?< ?0.3?0.4 of the optical radius r _(25)) 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)? r _(25)which 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 H I surface 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.