Bar formation and evolution in disc galaxies with gas and a triaxial halo: Morphology, bar strength and halo properties

TL;DR

This study uses N-body simulations to explore how gas content and halo shape influence bar formation and evolution in disc galaxies, revealing that gas fraction delays bar development and halo triaxiality affects bar strength and halo shape.

Contribution

It provides new insights into the combined effects of gas fraction and halo triaxiality on bar morphology, strength, and halo evolution in disc galaxies.

Findings

Gas-rich discs form bars later and have weaker bars.

Halo triaxiality accelerates initial bar formation but limits later bar growth.

Halo shape evolves towards sphericity, influenced by bar strength.

Abstract

We follow the formation and evolution of bars in N-body simulations of disc galaxies with gas and/or a triaxial halo. We find that both the relative gas fraction and the halo shape play a major role in the formation and evolution of the bar. In gas-rich simulations, the disc stays near-axisymmetric much longer than in gas-poor ones, and, when the bar starts growing, it does so at a much slower rate. Due to these two effects combined, large-scale bars form much later in gas-rich than in gas-poor discs. This can explain the observation that bars are in place earlier in massive red disc galaxies than in blue spirals. We also find that the morphological characteristics in the bar region are strongly influenced by the gas fraction. In particular, the bar at the end of the simulation is much weaker in gas-rich cases. In no case did we witness bar destruction. Halo triaxiality has a dual influence on bar strength. In the very early stages of the simulation it induces bar formation to start earlier. On the other hand, during the later, secular evolution phase, triaxial haloes lead to considerably less increase of the bar strength than spherical ones. The shape of the halo evolves considerably with time. The inner halo parts may become more elongated, or more spherical, depending on the bar strength. The main body of initially triaxial haloes evolves towards sphericity, but in initially strongly triaxial cases it stops well short of becoming spherical. Part of the angular momentum absorbed by the halo generates considerable rotation of the halo particles that stay located relatively near the disc for long periods of time. Another part generates halo bulk rotation, which, contrary to that of the bar, increases with time but stays small.