Vaulting the barrier: An intrinsic mechanism to fuel the gas beyond the nuclear ring into the central region of barred galaxies

TL;DR

This study reveals a three-dimensional gas inflow mechanism in barred galaxies where gas vaults over the nuclear ring, enabling it to reach the central few tens of parsecs and potentially fueling nuclear activity.

Contribution

The paper introduces a novel 3D gas inflow pathway in barred galaxies, absent in 2D models, that facilitates gas crossing the nuclear ring into the central region.

Findings

Gas vaulting occurs via vertical momentum gain, crossing the nuclear ring.

Inflow to the center mainly originates from gas outside the ring, not from within.

Successful inflow requires significant vertical excursion and angular momentum loss.

Abstract

Gas delivery to galactic centers powers nuclear starbursts and active galactic nuclei (AGNs), yet bar-driven inflow is generally expected to stall in a nuclear ring a few hundred parsecs across. Using three-dimensional Lagrangian hydrodynamic simulations in a fixed barred potential, we identify a bypass channel in which a fraction of the inflowing gas acquires vertical momentum, vaults across the ring, and reaches the inner few tens of parsecs. This pathway is absent in two-dimensional calculations, which instead predict long-lived stagnation at the ring. We find that the circumnuclear material within $\sim 50$ pc originates from gas initially located outside the ring ($\gtrsim 300$ pc), rather than from secondary inflow out of the ring itself. Successful delivery requires both a sufficiently large vertical excursion, $|z| \sim 100$ pc before encountering the ring, and substantial loss of azimuthal angular momentum $L_z$. The resulting inflow is organized rather than chaotic: center-reaching trajectories are confined to a limited spatial region set by the scale height of the ring gas. Most bar-driven gas still accumulates near the resonance and fuels star formation in the nuclear ring, but the vaulting stream selects a modest yet sufficient fraction that penetrates to the circumnuclear disk. These results suggest that intrinsically three-dimensional gas motions help link nuclear starbursts, AGN fueling, and the frequent misalignment of nuclear disks with respect to their host galaxies.