Modeling Thermal Dust Emission with Two Components: Application to the
  Planck HFI Maps
  We apply the Finkbeiner et al. (1999) two-component thermal dust emission
model to the Planck HFI maps. This parametrization of the far-infrared dust
spectrum as the sum of two modified blackbodies serves as an important
alternative to the commonly adopted single modified blackbody (MBB) dust
emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that
two-component models provide a better fit to the 100-3000 GHz emission than do
single-MBB models, though by a lesser margin than found by Finkbeiner et al.
(1999) based on FIRAS and DIRBE. We also derive full-sky 6.1' resolution maps
of dust optical depth and temperature by fitting the two-component model to
Planck 217-857 GHz along with DIRBE/IRAS 100 micron data. Because our
two-component model matches the dust spectrum near its peak, accounts for the
spectrum's flattening at millimeter wavelengths, and specifies dust temperature
at 6.1' FWHM, our model provides reliable, high-resolution thermal dust
emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse
sky regions, our two-component 100-217 GHz predictions are on average accurate
to within 2.2%, while extrapolating the Planck Collaboration (2013a) single-MBB
model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143
GHz and 7.9% at 217 GHz. We calibrate our two-component optical depth to
reddening, and compare with reddening estimates based on stellar spectra. We
find the dominant systematic problems in our temperature/reddening maps to be
zodiacal light on large angular scales and the cosmic infrared background
anisotropy on small angular scales.
