The Effect of Dark Matter Halo Shape on Bar Buckling and Boxy/Peanut Bulges

TL;DR

This study uses N-body simulations to explore how dark matter halo shapes influence bar formation, buckling, and bulge structures in galaxies, revealing that halo shape significantly affects the timing and characteristics of these features.

Contribution

It demonstrates for the first time how non-spherical dark matter halos impact bar buckling and bulge formation through detailed simulations.

Findings

Prolate halos lead to earlier and more frequent buckling events.

Bars in prolate halos are thicker and cause more disc heating.

Most observed barred galaxies likely have oblate or spherical halos.

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 halos and traced bar evolution for 8 Gyr. We find that bar formation is delayed in oblate halos, resulting in delayed buckling whereas bars form earlier in prolate halos 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 halos also show buckling signatures for the longest duration compared to spherical and oblate halos. Since ongoing buckling events are rarely observed, our study suggests that most barred galaxies may have more oblate or spherical halos rather than prolate halos. Our measurement of BPX structures also shows that prolate halos promote bar thickening and disc heating more than oblate and spherical halos.