Evolution of stellar bars in spinning dark matter haloes and stellar bulges

Abstract

We use numerical simulations to follow evolution of barred galaxies in a suite of models with progressively more massive stellar bulges, with bulge-to-total (disc+bulge) mass ratios of B/T ∼ 0–0.25, embedded in dark matter (DM) haloes with spin λ ∼ 0–0.09. We focus on models with a sequence of initial rotational support for bulges, and analyse their spinup and spindown. We find that (1) the presence of a bulge affects evolution of bars, i.e. the time-scale of bar instability, bar pattern speed, and its decay, and the vertical buckling instability. Bar strength is nearly independent of B/T in haloes with spin λ = 0, and is suppressed by a factor ∼2 for haloes with λ = 0.09; (2) The main effect of the bulge is the destruction of the harmonic core which affects the buckling; (3) The bulge plays a minor role in the exchange of angular momentum between the barred disc and the DM halo, during its spinup and spindown; (4) Buckling process triggers different response above/below the disc mid-plane, which anticorrelates with the bulge mass; (5) In spinning haloes, the buckling process has a prolonged amplitude tail, extending by few Gyr, as verified by measuring distortions in the Laplace plane; (6) Furthermore, as verified by orbital spectral analysis, the bulge gains its spin from the bar mainly via the inner Lindblad resonance, while losing it via a number of resonances lying between the outer and inner Lindblad resonance. The corollary is that we do not expect to find non-rotating bulges in barred galaxies.