Gas Dynamics and Outflow in the Barred Starburst Galaxy NGC 1808
  Revealed with ALMA
  NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear
region. To study the inflow and outflow processes related to star formation and
dynamical evolution of the galaxy, we have carried out \(^{12}\)CO (\(J=1-0\))
mapping observations of the central \(r\sim4\) kpc of NGC 1808 using the
Atacama Large Millimeter/submillimeter Array (ALMA). Four distinct components
of molecular gas are revealed at high spatial resolution of 2\arcsec
(\(\sim100\) pc): (1) a compact (\(r<200\) pc) circumnuclear disk (CND), (2)
\(r\sim500\) pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic
geometric and kinematic parameters are derived for the central 1-kpc region
using tilted-ring modeling. The derived rotation curve reveals multiple mass
components that include (1) a stellar bulge, (2) nuclear bar and molecular CND,
and (3) unresolved massive (\(\sim10^7~M_\sun\)) core. Two systemic velocities,
998 km s\(^{-1}\) for the CND and 964 km s\(^{-1}\) for the 500-pc ring, are
revealed, indicating a kinematic offset. The pattern speed of the primary bar,
derived by using a cloud-orbit model, is \(56\pm11\) km s\(^{-1}\)
kpc\(^{-1}\). Non-circular motions are detected associated with a nuclear
spiral pattern and outflow in the central 1-kpc region. The ratio of the mass
outflow rate to the star formation rate is \(\dot{M}_\mathrm{out}/SFR\sim0.2\)
in the case of optically thin CO (1-0) emission in the outflow, suggesting low
efficiency of star formation quenching.
