Untangling the Nature of Spatial Variations of Cold Dust Properties in
  Star Forming Galaxies
  We investigate the far-infrared (IR) dust emission for 20 local star forming
galaxies from the Key Insights on Nearby Galaxies: A Far-IR Survey with
Herschel (KINGFISH) sample. We model the far-IR/submillimeter spectral energy
distribution (SED) using images from Spitzer Space Telescope and Herschel Space
Observatory. We calculate the cold dust temperature (T(cold)) and emissivity
(beta) on a pixel by pixel basis (where each pixel ranges from 0.1-3 kpc^2)
using a two temperature modified blackbody fitting routine. Our fitting method
allows us to investigate the resolved nature of temperature and emissivity
variations by modeling from the galaxy centers to the outskirts (physical
scales of ~15-50 kpc, depending on the size of the galaxy). We fit each SED in
two ways: (1) fit T(cold) and beta simultaneously, (2) hold beta constant and
fit T(cold). We compare T(cold) and beta with star formation rates (calculated
from L(Halpha) and L(24)), the luminosity of the old stellar population (traced
through L(3.6), and the dust mass surface density (traced by 500 micron
luminosity, L(500)). We find a significant trend between SFR/L(500) and
T(cold), implying that the flux of hard UV photons relative to the amount of
dust is significantly contributing to the heating of the cold, or diffuse, dust
component. We also see a trend between L(3.6)/L(500) and beta, indicating that
the old stellar population contributes to the heating at far-IR/submillimeter
wavelengths. Finally, we find that when beta is held constant, T(cold) exhibits
a strongly decreasing radial trend, illustrating that the shape of the far-IR
SED is changing radially through a galaxy, thus confirming on a sample almost
double in size the trends observed in Galametz et al. (2012).
