Constraints on the Minor Merging and Star Formation History of the
  Wolf-Rayet Galaxy NGC 5430 Through Observations
  We used multi-wavelength analysis of the newly observed molecular gas (12CO
and 13CO (1-0)) with interferometer CARMA and archival star formation tracers
to constrain the interaction, merging, and star formation history of an
off-center minor merger, a three-spiral barred galaxy NGC 5430 and its
satellite embedded in the bar. Morphology of the molecular gas in the bar of
NGC 5430 shows minimal signs of recent interactions in our resolution. The
apparent morphological remnant of the past galaxy interaction is an asymmetric
spiral arm, containing more molecular gas and exhibiting higher star formation
rate (SFR) surface density than the two primary arms. Rotation curve analysis
suggests that NGC 5430 and its satellite collided several Gyr ago. History of
star formation was constrained by using SFRs that trace different timescales
(infrared, radio continuum, and H-alpha). The collision occurred 5 - 10 Myr
ago, triggering a transient off-center starburst of Wolf-Rayet stars at the
eastern bar end. In the past, the global SFR during the Wolf-Rayet starburst
peaked at 35 Msun/yr. At present, the merger-driven starburst is rapidly
decaying and the current global SFR has decreased to the Galactic value. The
SFR will continue to decay as suggested by the present amount of dense gas
(traced by HCN (1-0)). Nonetheless, the global SFR is still dominated by the
Wolf-Rayet region rather than the circumnuclear region. Compared with other
barred galaxies, the circumnuclear region exhibits particularly low dense gas
fraction, low star formation activity and high concentration of gas. Physical
properties of the molecular gas are inferred by using the large velocity
gradient (LVG) calculations. The initial mass ratio of the NGC 5430 and its
satellite are suggested to be in the intermediate ratio range of 7:1-20:1.
