Effects of Spiral Arms on Star Formation in Nuclear Rings of Barred-spiral Galaxies

TL;DR

Hydrodynamic simulations reveal that slow-rotating spiral arms significantly enhance and extend star formation in nuclear rings of barred-spiral galaxies by facilitating gas inflow, leading to larger rings and stronger dust lanes.

Contribution

This study demonstrates that slow-rotating spiral arms can efficiently transport gas inward, substantially increasing and prolonging star formation in nuclear rings, a novel insight into galaxy dynamics.

Findings

Spiral arms rotating slower than the bar enhance gas inflow.

Arm-driven gas inflow increases star formation rate by a factor of 3-20.

Nuclear rings are approximately 45% larger in slow-arm models.

Abstract

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.