Benchmarking Dust Emission Models in M101
  We present a comparative study of four physical dust models and two
single-temperature modified blackbody models by fitting them to the resolved
WISE, Spitzer, and Herschel photometry of M101 (NGC 5457). Using identical data
and a grid-based fitting technique, we compare the resulting dust and radiation
field properties derived from the models. We find that the dust mass yielded by
the different models can vary by up to factor of 3 (factor of 1.4 between
physical models only), although the fits have similar quality. Despite
differences in their definition of the carriers of the mid-IR aromatic
features, all physical models show the same spatial variations for the
abundance of that grain population. Using the well determined metallicity
gradient in M101 and resolved gas maps, we calculate an approximate upper limit
on the dust mass as a function of radius. All physical dust models are found to
exceed this maximum estimate over some range of galactocentric radii. We show
that renormalizing the models to match the same Milky Way high latitude cirrus
spectrum and abundance constraints can reduce the dust mass differences between
models and bring the total dust mass below the maximum estimate at all radii.
