The formation of stellar nuclear discs in bar-induced gas inflows

TL;DR

This paper uses high-resolution simulations to study how gas inflows driven by galactic bars lead to the formation of nuclear stellar discs, highlighting their properties and observational signatures.

Contribution

It demonstrates that gas dissipation and bar-driven inflows are key to forming nuclear discs with distinct kinematic and chemical properties, supported by simulation and observational comparison.

Findings

Nuclear discs are younger, thinner, and more metal-rich than surrounding regions.

They are elliptical and orthogonal to the bar structure.

Kinematic signatures are subtle, but metallicity and age maps clearly reveal the discs.

Abstract

The role of gas in the mass assembly at the nuclei of galaxies is still subject to some uncertainty. Stellar nuclear discs bridge the gap between the large-scale galaxy and the central massive objects that reside there. Using a high resolution simulation of a galaxy forming out of gas cooling and settling into a disc, we study the formation and properties of nuclear discs. Gas, driven to the centre by a bar, settles into a rotating star-forming nuclear disc (ND). This ND is thinner, younger, kinematically cooler, and more metal-rich than the surrounding bar. The ND is elliptical and orthogonal to the bar. The complex kinematics in the region of the ND are a result of the superposition of older stars streaming along the bar and younger stars circulating within the ND. The signature of the ND is therefore subtle in the kinematics. Instead the ND stands out clearly in metallicity and age maps. We compare the model to the density and kinematics of real galaxies with NDs finding qualitative similarities. Our results suggest that gas dissipation is very important for forming nuclear structures.