Dust emission profiles of DustPedia galaxies

Abstract

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 μm, 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 μm is 0.67 ± 0.37 (187 galaxies are fitted with n<SUP>250</SUP> ≤ 0.75, 87 galaxies have 0.75 < n<SUP>250</SUP> ≤ 1.25, and 46 - with n<SUP>250</SUP> > 1.25). Most observed profiles exhibit a depletion in the inner region (at r < 0.3-0.4 of the optical radius r<SUB>25</SUB>) 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<SUB>25</SUB> 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 HI 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. <P />DustPedia is a project funded by the EU under the heading "Exploitation of space science and exploration data". It has the primary goal of exploiting existing data in the Herschel Space Observatory and Planck Telescope databases.The tables with the results are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A132">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A132