How Nested Bars Enhance, Modulate, and are Destroyed by Gas Inflows

TL;DR

This study uses high-resolution hydrodynamical simulations to explore how nested bars influence gas inflows in galaxies, revealing their role in fueling black holes, star formation, and their eventual dissolution.

Contribution

It provides new insights into the dynamics of nested bars, demonstrating their impact on gas flow, star formation, and their decay over time through detailed simulations.

Findings

Inner bars drive gas from nuclear rings to galaxy centers.

Gas inflow stalls at nuclear rings in single-barred galaxies.

Inner bars weaken and dissolve over a few billion years.

Abstract

Gas flows in the presence of two independently-rotating nested bars remain not fully understood, which is likely to play an important role in fueling the central black hole. We use high-resolution hydrodynamical simulations with detailed models of subgrid physics to study this problem. Our results show that the inner bar in double-barred galaxies can help drive gas flow from the nuclear ring to the center. In contrast, gas inflow usually stalls at the nuclear ring in single-barred galaxies. The inner bar causes a quasi-periodic inflow with a frequency determined by the difference between the two bar pattern speeds. We find that the star formation rate is higher in the model with two bars than in that with one bar. The inner bar in our model gradually weakens and dissolves due to gas inflow over a few billion years. Star formation produces metal-rich/$\alpha$-poor stars which slows the weakening of the inner bar, but does not halt its eventual decay. We also present a qualitative comparison of the gas morphology and kinematics in our simulations with those of observed double-barred galaxies.