The formation and evolution of bars in low surface brightness galaxies with cold dark matter haloes

Abstract

We perform several high-resolution simulations of low surface brightness galaxies (LSBGs) embedded in cold dark matter haloes to study how likely bar formation is in such systems. The behaviour of various collisionless galaxy models is studied both in isolation and in the presence of a large perturbing satellite. We also consider models with a dominant gaseous component in the disc. We find that in general bar formation requires disc masses at least a factor of 2 higher than those inferred for LSBGs under the assumption of a normal stellar mass-to-light ratio. Instead, if LSBGs have fairly light, low surface density discs, they are stable to the formation of a stellar bar within NFW (Navarro-Frenk-White) haloes spanning a range of concentrations. However, a purely gaseous light disc can form a bar for realistic temperatures provided that cooling is very efficient (we adopt an isothermal equation of state) and that the halo has a very low concentration, c < 5. The bars that form in these low surface brightness (LSB) models are significantly shorter than the typical halo scale radius - their overall angular momentum content might be too low to affect significantly the inner dark halo structure. Once formed, all the bars evolve into bulge-like structures in only a few gigayears and can excite spiral patterns in the surrounding disc component. The recently discovered red LSBGs show significant non-axisymmetric structure and bulge-like components, and share many of their structural properties with the final states of our LSB models with massive discs. Our results imply that a bulge-like component must be present in any LSBG that ever went bar-unstable in the past.