Mass Distribution and Bar Formation in Growing Disk Galaxy Models

TL;DR

This study uses idealized simulations to explore how galaxy disks grow and tend to form bars, revealing that bar formation is a persistent issue in galaxy evolution, especially in gas-poor systems.

Contribution

The paper demonstrates that bar formation occurs readily in growing disk galaxy models and persists throughout evolution, challenging previous assumptions about galaxy stability.

Findings

Growing disks frequently form strong bars.

Bar formation occurs even after initial bars are destroyed.

Spiral activity maintains smooth density profiles despite bar formation.

Abstract

We report idealized simulations that mimic the growth of galaxy disks embedded in responsive halos and bulges. The disks manifested an almost overwhelming tendency to form strong bars that we found very difficult to prevent. We found that fresh bars formed in growing disks after we had destroyed the original, indicating that bar formation also afflicts continued galaxy evolution, and not just the early stages of disk formation. This behavior raises still more insistently the previously unsolved question of how some galaxies avoid bars. Since our simulations included only collisionless star and halo particles, our findings may apply to gas-poor galaxies only; however the conundrum persists for the substantial unbarred fraction of those galaxies. Our original objective was to study how internal dynamics rearranged the distribution of mass in the disk as a generalization of our earlier study with rigid spherical components. With difficulty, we were able to construct some models that were not strongly influenced by bars, and found that halo compression, and angular momentum exchange with the disk did not alter our earlier conclusion that spiral activity is largely responsible for creating smooth density profiles and rotation curves.