The Impact of Classical Bulges on Stellar Bars and Box-Peanut-X-Features in Disk Galaxies

TL;DR

This study investigates how classical bulges influence the development of stellar bars and box-peanut X-features in disk galaxies, revealing that bulge mass affects resonance structures and orbit dynamics without needing resonance trapping.

Contribution

It provides new insights into the role of bulge mass in shaping bar and BPX structures through resonance interactions, based on N-body simulations and frequency analysis.

Findings

More massive bulges lead to stronger, more extended bars.

BPX formation is driven by resonance interactions of bar-supporting orbits.

Resonance trapping is not necessary for BPX development.

Abstract

Galactic bars and their associated resonances play a significant role in shaping galaxy evolution. Resulting resonance-driven structures, like the vertically extended Boxy/Peanut X-Feature (BPX), then serve as a useful probe of the host galaxy's history. In this study, we quantify the impact of a classical bulge on the evolution of the bar and the growth of bar resonance structures. This is accomplished with a suite of isolated N-body disk galaxy simulations with bulge mass fractions ranging from 0% to 16% of the disk mass. We apply frequency analysis to the stellar orbits to analyze the variations in resonance structure evolution. Our findings indicate that a more massive initial bulge leads to the formation of a stronger and more extended bar and that each bar drives the formation of a prominent associated BPX through resonance passage. In this work, we present evidence that the formation of a BPX is driven by planar, bar-supporting orbits evolving through interaction with horizontal and vertical bar-resonances. More orbits become vertically extended when these resonances intersect, and the rate of the orbits passing through resonance is moderated by the overall fraction of vertically extended orbits. A significant bulge stabilizes the fraction of vertically extended orbits, preventing sudden resonance-induced changes. Crucially, neither sudden resonance intersection nor prolonged resonance trapping is required for BPX formation.