Effects of Spiral Arms on Star Formation in Nuclear Rings of
  Barred-spiral Galaxies
  We use hydrodynamic simulations to study the effect of spiral arms on the
star formation rate (SFR) occurring in nuclear rings of barred-spiral galaxies.
We find that spiral arms can be an efficient means of gas transport from the
outskirts to the central parts, provided that the arms are rotating slower than
the bar. While the ring star formation in models with no-arm or corotating arms
is active only during about the bar growth phase, arm-driven gas accretion
makes the ring star formation both enhanced and prolonged significantly in
models with slow-rotating arms. The arm-enhanced SFR is larger by a factor of ~
3-20 than in the no-arm model, with larger values corresponding to stronger and
slower arms. Arm-induced mass inflows also make dust lanes stronger. Nuclear
rings in slow-arm models are ~ 45% larger than in the no-arm counterparts. Star
clusters that form in a nuclear ring exhibit an age gradient in the azimuthal
direction only when the SFR is small, whereas no noticeable age gradient is
found in the radial direction for models with arm-induced star formation.
