Effects of Varying Mass Inflows on Star Formation in Nuclear Rings of Barred Galaxies

TL;DR

This study uses hydrodynamic simulations to explore how varying mass inflows influence star formation in nuclear rings of barred galaxies, revealing the roles of inflow variability and supernova feedback in shaping star formation patterns.

Contribution

It demonstrates how time-varying and asymmetric inflows affect star formation rates and asymmetries in nuclear rings, incorporating effects of supernova feedback and self-regulation theory.

Findings

Oscillating inflow causes large, quasi-periodic SFR variations.

Supernova feedback induces small-amplitude, rapid SFR fluctuations.

Asymmetry in inflow does not always produce asymmetric star formation.

Abstract

Observations indicate that the star formation rate (SFR) of nuclear rings varies considerably with time and is sometimes asymmetric rather than being uniform across a ring. To understand what controls temporal and spatial distributions of ring star formation, we run semi-global, hydrodynamic simulations of nuclear rings subject to time-varying and/or asymmetric mass inflow rates. These controlled variations in the inflow lead to variations in the star formation, while the ring orbital period ($18\,{\rm Myr}$) and radius ($600\,{\rm pc}$) remain approximately constant. We find that both the mass inflow rate and supernova feedback affect the ring SFR. An oscillating inflow rate with period $\Delta \tau_\text{in}$ and amplitude 20 causes large-amplitude (a factor of $\gtrsim 5$), quasi-periodic variations of the SFR, when $\Delta \tau_\text{in} \gtrsim 50\,{\rm Myr}$. We find that the time-varying ISM weight and midplane pressure track each other closely, establishing an instantaneous vertical equilibrium. The measured time-varying depletion time is consistent with the prediction from self-regulation theory provided the time delay between star formation and supernova feedback is taken into account. The supernova feedback is responsible only for small-amplitude (a factor of $\sim 2$) fluctuations of the SFR with a timescale $\lesssim 40\,{\rm Myr}$. Asymmetry in the inflow rate does not necessarily lead to asymmetric star formation in nuclear rings. Only when the inflow rate from one dust lane is suddenly increased by a large factor, the rings undergo a transient period of lopsided star formation.