Morphologies arising from the gas flow in the innermost kiloparsec of barred galaxy models

TL;DR

This study investigates how gas flow dynamics and gravitational potential parameters influence the formation of nuclear rings and spirals in the central kiloparsec of barred galaxies, emphasizing the importance of hydrodynamics.

Contribution

It demonstrates that gas morphology depends heavily on hydrodynamic processes and provides insights into how various potential parameters affect nuclear structures.

Findings

Gas morphology varies significantly with sound speed.

Hydrodynamics play a crucial role in structure formation.

Optimal model alignment with observations occurs at 20 km/s sound speed.

Abstract

Context. We study a series of response models to investigate the formation of specific morphological features in the central 1 kpc region of the gas component in barred spiral galaxies. Aims. We aim to understand how structures, such as nuclear rings and spirals, form by varying the parameters of a general gravitational potential and gas properties. Our goal is to determine how much the shape of these structures is driven by the orbital dynamics of the models compared to the influence of the hydrodynamics of the gas. In particular, we examine the effects of the bar strength, bar shape, pattern speed, and central density, as well as their mutual interdependence. Methods. We modeled the gas flow using hydrodynamical simulations run with the Eulerian RAMSES code. The underlying gravitational potential was a two-dimensional Ferrers bar and the gas was considered to be isothermal. Alongside analyzing the gas response to the imposed gravitational potentials, we carried out orbital studies for all models. This involved assessing the shapes and stability of periodic orbits and analyzing the distribution of regular versus chaotic regions within the systems. Results. The parameters of the gravitational potential alone are insufficient to accurately predict the gas dynamics in a system. The morphology of the gaseous response varies substantially with changes in sound speed, emphasizing the fundamental role of hydrodynamic processes in determining the structure of the gas within the central region. We identify the factors that affect the morphology of nuclear rings and trailing and leading nuclear spirals. The best alignment between our models and structures observed in local barred galaxies is achieved by assuming a sound speed of $c_s=20\,\rm{km\,s^{-1}}$.