ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC
  5179$^\star$
  We present our high-resolution
($0^{\prime\prime}.15\times0^{\prime\prime}.13$, $\sim$34 pc) observations of
the CO(6-5) line emission, which probes the warm and dense molecular gas, and
the 434 $\mu$m dust continuum emission in the nuclear region of the starburst
galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The
CO(6-5) emission is spatially distributed in filamentary structures with many
dense cores and shows a velocity field that is characteristic of a
circum-nuclear rotating gas disk, with 90% of the rotation speed arising within
a radius of $\lesssim150$ pc. At the scale of our spatial resolution, the
CO(6-5) and dust emission peaks do not always coincide, with their surface
brightness ratio varying by a factor of $\sim$10. This result suggests that
their excitation mechanisms are likely different, as further evidenced by the
Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and
Pa-$\alpha$ equivalent width. Within the nuclear region (radius$\sim$300 pc)
and with a resolution of $\sim$34 pc, the CO line flux (dust flux density)
detected in our ALMA observations is $180\pm18$ Jy km/s ($71\pm7$ mJy), which
account for 22% (2.4%) of the total value measured by Herschel.
