Radial distribution of dust, stars, gas, and star-formation rate in
  DustPedia face-on galaxies
  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. This study is
performed by exploiting the multi-wavelength, from UV to sub-mm bands,
DustPedia database, 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 (alpha_CO) per galaxy by using dust and gas mass profiles. Although each
galaxy has its own peculiar behaviour, we identified a common trend of the
exponential scale-lengths vs. wavelength. On average, the scale-lengths
normalized to the B-band 25 mag/arcsec^2 radius decrease from UV to 70 micron,
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 from IRAC data and the 3.6 micron 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 3.6 micron scale-length tend to increase from earlier to later types,
the scale-length at 70 micron tends to be smaller than that at longer sub-mm
wavelength with ratios between longer sub-mm wavelengths and 70 micron that
decrease with increasing T. The scale-length ratio of SFR and stars shows a
weak increasing trend towards later types.
