Tidally induced bars in gas-rich dwarf galaxies orbiting the Milky Way

TL;DR

This study uses N-body/SPH simulations to investigate how tidal interactions induce bar formation in gas-rich dwarf galaxies orbiting the Milky Way, revealing that gas content influences bar longevity and properties.

Contribution

It demonstrates that tidal forces can induce bars in dwarf galaxies regardless of gas fraction, and explores how gas content and orbital orientation affect bar evolution.

Findings

Bars form at first pericenter regardless of gas fraction.

Gas remains axisymmetric and unaffected by the bar.

Bar properties depend on orbital orientation and gas content.

Abstract

Bars in galaxies may form not only through instability, but also as a result of an interaction with another galaxy. In particular, they may appear in disky dwarf galaxies interacting with Milky Way-like galaxies. Here we report the results of N-body/SPH simulations of such dwarfs orbiting in the static potential of a larger galaxy. We used several models of the dwarf galaxy, all of the same mass, but covering a large range of gas fractions: 0, 30 and 70%. We also tested the impact of subgrid star formation processes. In all cases bars of similar length formed in the stellar disk of the dwarfs at the first pericenter passage. However, unexpectedly, the gaseous component remained approximately axisymmetric and unaffected by the bar potential. The bar properties did not change significantly between two consecutive pericenters. The impact of the later encounters with the host depends strongly on the exact orientation of the bar at the pericenter. When the bar is spun up by the tidal force torque, it is also shortened. Conversely, if it is slowed down, it gets longer. In the models with a low gas fraction the bars were more pronounced and survived until the end of the simulations, while in the dwarfs with a high gas fraction the bars were destroyed after the second or third pericenter passage. In terms of the ratio of the corotation radius to the bar length, the bars are slow, and remain so independently of the encounters with the host.