  We present observations of the $^{12}$CO(6-5) line and 686GHz continuum
emission in NGC253 with the Submillimeter Array at an angular resolution of
~4arcsec. The $^{12}$CO(6-5) emission is clearly detected along the disk and
follows the distribution of the lower $^{12}$CO line transitions with little
variations of the line ratios in it. A large-velocity gradient analysis
suggests a two-temperature model of the molecular gas in the disk, likely
dominated by a combination of low-velocity shocks and the disk wide PDRs. Only
marginal $^{12}$CO(6-5) emission is detected in the vicinity of the expanding
shells at the eastern and western edges of the disk. While the eastern shell
contains gas even warmer (T$_{\rm kin}$>300~K) than the hot gas component
(T$_{\rm kin}$=300K) of the disk, the western shell is surrounded by gas much
cooler (T$_{\rm kin}$=60K) than the eastern shell but somewhat hotter than the
cold gas component of the disk (for similar H$_2$ and CO column densities),
indicative of different (or differently efficient) heating mechansisms. The
continuum emission at 686GHz in the disk agrees well in shape and size with
that at lower (sub-)millimeter frequencies, exhibiting a spectral index
consistent with thermal dust emission. We find dust temperatures of ~10-30K and
largely optically thin emission. However, our fits suggest a second (more
optically thick) dust component at higher temperatures (T$_{\rm d}$>60K),
similar to the molecular gas. We estimate a global dust mass of ~10$^6$Msun for
the disk translating into a gas-to-dust mass ratio of a few hundred consistent
with other nearby active galaxies.

Astrophysics of Galaxies