Radial distribution of stars, gas and dust in SINGS galaxies. II.
  Derived dust properties
  We present a detailed analysis of the radial distribution of dust properties
in the SINGS sample, performed on a set of UV, IR and HI surface brightness
profiles, combined with published molecular gas profiles and metallicity
gradients. The internal extinction, derived from the TIR-to-FUV luminosity
ratio, decreases with radius, and is larger in Sb-Sbc galaxies. The TIR-to-FUV
ratio correlates with the UV spectral slope beta, following a sequence shifted
to redder UV colors with respect to that of starbursts. The star formation
history (SFH) is identified as the main driver of this departure. We have also
derived radial profiles of the total dust mass surface density, the fraction of
the dust mass contributed by PAHs, the fraction of the dust mass heated by very
intense starlight and the intensity of the radiation field heating the grains.
The dust profiles are exponential, their radial scale-length being constant
from Sb to Sd galaxies (only ~10% larger than the stellar scale-length). Many
S0/a-Sab galaxies have central depressions in their dust radial distributions.
The PAH abundance increases with metallicity for 12+\log(O/H)<9, and at larger
metallicities the trend flattens and even reverses, with the SFH being a
plausible underlying driver for this behavior. The dust-to-gas ratio is also
well correlated with metallicity and therefore decreases with galactocentric
radius.
