Effects of Mass Inflows on Star Formation in Nuclear Rings at Galaxy Centers

Observations suggest that the star formation rate (SFR) in nuclear rings at galaxy centers varies significantly over time. To understand what determines the ring SFR and causes its variability, we run semi-global, hydrodynamic simulations of nuclear rings subject to predetermined (and controllable) mass inflow rates. We adopt the TIGRESS framework of Kim & Ostriker to handle radiative heating and cooling, star formation, and related supernova feedback. We find that a constant inflow rate leads to very steady and persistent star formation, with the SFR tightly correlated with the inflow rate. On the other hand, an oscillating inflow rate with period dT causes large-amplitude, quasi-periodic variations of the SFR, when dT > ~50 Myr. The supernova feedback is responsible only for small-amplitude (a factor of ~2) fluctuations of the SFR with a timescale ~40 Myr. Our results imply that long (> ~50 Myr) timescale, large-amplitude variations in the ring SFR are likely driven by variations in the mass inflow rate.