The effect of dark matter halo shape on bar buckling and boxy/peanut bulges

Abstract

It is well established that bars evolve significantly after they form in galaxy discs, often changing shape both in and out of the disc plane. In some cases they may bend or buckle out of the disc plane resulting in the formation of boxy/peanut/x-shape bulges. In this paper we show that the dark matter halo shape affects bar formation and buckling. We have performed N-body simulations of bar buckling in non-spherical dark matter haloes and traced bar evolution for 8 Gyr. We find that bar formation is delayed in oblate haloes, resulting in delayed buckling whereas bars form earlier in prolate haloes leading to earlier buckling. However, the duration of first buckling remains almost comparable. All the models show two buckling events but the most extreme prolate halo exhibits three distinct buckling features. Bars in prolate haloes also show buckling signatures for the longest duration compared to spherical and oblate haloes. Since ongoing buckling events are rarely observed, our study suggests that most barred galaxies may have more oblate or spherical haloes rather than prolate haloes. Our measurement of BPX structures also shows that prolate haloes promote bar thickening and disc heating more than oblate and spherical haloes.