Dynamically Driven Inflow onto the Galactic Center and its Effect upon Molecular Clouds

TL;DR

This study uses hydrodynamic simulations to analyze how gas inflow driven by the Galactic bar affects molecular cloud formation and dynamics in the Milky Way's Central Molecular Zone, revealing inflow efficiency, cloud collision dynamics, and rotation characteristics.

Contribution

The paper presents the first hydrodynamic simulations modeling the Milky Way's bar-driven inflow without gas self-gravity or star formation, quantifying inflow efficiency and cloud behavior.

Findings

Approximately 30% of dust lane mass accretes onto the CMZ.

Inflow rate onto the CMZ is estimated at 0.8±0.6 M_sun/yr.

About 52% of clouds are strongly counter-rotating, 7% strongly co-rotating.

Abstract

The Galactic bar plays a critical role in the evolution of the Milky Way's Central Molecular Zone (CMZ), driving mass inward toward the Galactic Center via gas flows known as dust lanes. To explore the interaction between the CMZ and the dust lanes, we run hydrodynamic simulations in AREPO, modeling the potential of the Milky Way's bar in the absence of gas self-gravity and star formation physics, and we study the flows of mass using Monte Carlo tracer particles. We estimate the efficiency of the inflow via the dust lanes, finding that only about a third (30$\pm$12%) of the dust lanes' mass initially accretes onto the CMZ, while the rest overshoots and accretes later. Given observational estimates of the amount of gas within the Milky Way's dust lanes, this suggests that the true total inflow rate onto the CMZ is 0.8$\pm$0.6 M$_\odot$~yr$^{-1}$. Clouds in this simulated CMZ have sudden peaks in their average density near the apocenter, where they undergo violent collisions with inflowing material. While these clouds tend to counter-rotate due to shear, co-rotating clouds occasionally occur due to the injection of momentum from collisions with inflowing material (~52% are strongly counter-rotating, and ~7% are strongly co-rotating of the 44 cloud sample). We investigate the formation and evolution of these clouds, finding that they are fed by many discrete inflow events, providing a consistent source of gas to CMZ clouds even as they collapse and form stars