Enhanced dust heating in the bulges of early-type spiral galaxies
  Stellar density and bar strength should affect the temperatures of the cool
(T ~ 20-30 K) dust component in the inner regions of galaxies, which implies
that the ratio of temperatures in the circumnuclear regions to the disk should
depend on Hubble type. We investigate the differences between cool dust
temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting
models to measurements between 70 and 500 microns. We attempt to quantify
temperature trends in nearby disk galaxies, with archival data from
Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired
during the first phases of the Herschel observations for the KINGFISH (key
insights in nearby galaxies: a far-infrared survey with Herschel) sample. We
fit single-temperature modified blackbodies to far-infrared and submillimeter
measurements of the central and disk regions of galaxies to determine the
temperature of the component(s) emitting at those wavelengths. We present the
ratio of central-region-to-disk-temperatures of the cool dust component of 13
nearby galaxies as a function of morphological type. We find a significant
temperature gradient in the cool dust component in all galaxies, with a mean
center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures
in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological
types earlier than Sc, and only 9(+/-3)% hotter for later types. The
temperature ratio is also correlated with bar strength, with only strongly
barred galaxies having a ratio over 1.2. The strong radiation field in the high
stellar density of a galactic bulge tends to heat the cool dust component to
higher temperatures, at least in early-type spirals with relatively large
bulges, especially when paired with a strong bar.
