2017A&A...605A..18C

Aims. The purpose of this work is the characterization of the radial distribution of dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18 face-on spiral galaxies extracted from the DustPedia sample.
Methods. This study is performed by exploiting the multi-wavelength DustPedia database, from ultraviolet (UV) to sub-millimeter bands, in addition to molecular (¹²CO) and atomic (HI) gas maps and metallicity abundance information available in the literature. We fitted the surface-brightness profiles of the tracers of dust and stars, the mass surface-density profiles of dust, stars, molecular gas, and total gas, and the SFR surface-density profiles with an exponential curve and derived their scale-lengths. We also developed a method to solve for the CO-to-H₂ conversion factor (α_CO) per galaxy by using dust- and gas-mass profiles.
Results. Although each galaxy has its own peculiar behavior, we identified a common trend of the exponential scale-lengths versus wavelength. On average, the scale-lengths normalized to the B-band 25mag/arcsec² radius decrease from UV to 70µm, from 0.4 to 0.2, and then increase back up to ∼0.3 at 500 microns. The main result is that, on average, the dust-mass surface-density scale-length is about 1.8 times the stellar one derived fromIRAC data and the 3.6µm surface brightness, and close to that in the UV. We found a mild dependence of the scale-lengths on the Hubble stage T: the scale-lengths of the Herschel bands and the 3.6µm scale-length tend to increase from earlier to later types, the scale-length at 70µm tends to be smaller than that at longer sub-mm wavelength with ratios between longer sub-mm wavelengths and 70µm that decrease with increasing T. The scale-length ratio of SFR and stars shows a weak increasing trend towards later types. Our α_CO determinations are in the range (0.3-9)M_☉/pc²/(K.km/s), almost invariant by using a fixed dust-to-gas ratio mass (DGR) or a DGR depending on metallicity gradient.