Mapping far-IR emission from the central kiloparsec of NGC 1097
  Using photometry of NGC 1097 from the Herschel PACS (Photodetector Array
Camera and Spectrometer) instrument, we study the resolved properties of
thermal dust continuum emission from a circumnuclear starburst ring with a
radius ~ 900 pc. These observations are the first to resolve the structure of a
circumnuclear ring at wavelengths that probe the peak (i.e. lambda ~ 100
micron) of the dust spectral energy distribution. The ring dominates the
far-infrared (far-IR) emission from the galaxy - the high angular resolution of
PACS allows us to isolate the ring's contribution and we find it is responsible
for 75, 60 and 55% of the total flux of NGC 1097 at 70, 100 and 160 micron,
respectively. We compare the far-IR structure of the ring to what is seen at
other wavelengths and identify a sequence of far-IR bright knots that
correspond to those seen in radio and mid-IR images. The mid- and far-IR band
ratios in the ring vary by less than +/- 20% azimuthally, indicating modest
variation in the radiation field heating the dust on ~ 600 pc scales. We
explore various explanations for the azimuthal uniformity in the far-IR colors
of the ring including a lack of well-defined age gradients in the young stellar
cluster population, a dominant contribution to the far-IR emission from dust
heated by older (> 10 Myr) stars and/or a quick smoothing of local enhancements
in dust temperature due to the short orbital period of the ring. Finally, we
improve previous limits on the far-IR flux from the inner ~ 600 pc of NGC 1097
by an order of magnitude, providing a better estimate of the total bolometric
emission arising from the active galactic nucleus and its associated central
starburst.
