GAS DYNAMICS AND OUTFLOW IN THE BARRED STARBURST GALAXY NGC 1808 REVEALED WITH ALMA

Abstract

ABSTRACT 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 12CO ( ) mapping observations of the central r ∼ 4 kpc of NGC 1808 using the Atacama Large Millimeter/submillimeter Array. Four distinct components of molecular gas are revealed at high spatial resolution of 2″ (∼100 pc): (1) a compact (r < 200 pc) circumnuclear disk (CND), (2) r ∼ 500 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) a nuclear bar and molecular CND, and (3) an unresolved massive (∼107 M ⊙) 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 ± 11 km s−1 kpc−1. Noncircular 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 in the case of optically thin CO (1–0) emission in the outflow, suggesting low efficiency of star formation quenching.