Bars in dark matter-dominated dwarf galaxy discs

TL;DR

This study reveals that many dark matter-dominated dwarf galaxy discs in simulations develop weak bars that influence gas kinematics, with implications for interpreting observations of such galaxies.

Contribution

It demonstrates that bar-like structures can form in dark matter-dominated dwarf galaxies and affect their gas motions, a phenomenon not widely recognized before.

Findings

Weak stellar bars are common in simulated dwarf discs.

Bar shapes reflect dark matter halo ellipticity and rotation.

Simulated bisymmetric flows are comparable to observed galaxy features.

Abstract

We study the shape and kinematics of simulated dwarf galaxy discs in the APOSTLE suite of $\Lambda$CDM cosmological hydrodynamical simulations. We find that a large fraction of these gas-rich, star-forming discs show weak bars in their stellar component, despite being dark matter-dominated systems. The bar pattern shape and orientation reflect the ellipticity of the dark matter potential, and its rotation is locked to the slow figure rotation of the triaxial dark halo. The bar-like nature of the potential induces non-circular motions in the gas component, including strong bisymmetric flows that can be readily seen as m=3 harmonic perturbations in the HI line-of-sight velocity fields. Similar bisymmetric flows are seen in many galaxies of the THINGS and LITTLE THINGS surveys, although on average their amplitudes are a factor of ~2 weaker than in our simulated discs. Our results indicate that bar-like patterns may arise even when baryons are not dominant, and that they are common enough to warrant careful consideration when analyzing the gas kinematics of dwarf galaxy discs.