Hot dust in Panchromatic SED Fitting: Identification of AGN and improved
  galaxy properties
  Forward modeling of the full galaxy SED is a powerful technique, providing
self-consistent constraints on stellar ages, dust properties, and
metallicities. However, the accuracy of these results is contingent on the
accuracy of the model. One significant source of uncertainty is the
contribution of obscured AGN, as they are relatively common and can produce
substantial mid-IR (MIR) emission. Here we include emission from dusty AGN
torii in the Prospector SED-fitting framework, and fit the UV-IR broadband
photometry of 129 nearby galaxies. We find that 10% of the fitted galaxies host
an AGN contributing $>$10% of the observed galaxy MIR luminosity. We
demonstrate the necessity of this AGN component in the following ways. First,
we compare observed spectral features to spectral features predicted from our
model fit to the photometry. We find that the AGN component greatly improves
predictions for observed H$\alpha$ and H$\beta$ luminosities, as well as
mid-infrared Akari and Spitzer/IRS spectra. Second, we show that inclusion of
the AGN component changes stellar ages and SFRs by up to a factor of 10, and
dust attenuations by up to a factor of 2.5. Finally, we show that the strength
of our model AGN component correlates with independent AGN indicators,
suggesting that these galaxies truly host AGN. Notably, only 46% of the
SED-detected AGN would be detected with a simple MIR color selection. Based on
these results, we conclude that SED models which fit MIR data without AGN
components are vulnerable to substantial bias in their derived parameters.
