Bar Formation from Galaxy Flybys

TL;DR

Flyby interactions between galaxies can induce long-lasting stellar bars, suggesting that galaxy interactions play a significant role in secular evolution processes.

Contribution

This study provides the first simulation-based evidence that galaxy flybys can trigger and sustain bar formation in disk galaxies.

Findings

Flybys can induce bars with ellipticities >0.5.

Bars formed during flybys can last for at least 5 Gyr.

Both primary and secondary galaxies can develop bars during flybys.

Abstract

Recently, both simulations and observations have revealed that flybys - fast, one-time interactions between two galaxy halos - are surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three co-planer flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar with bars forming in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities >0.5, sizes on the order of the host disk's scale length, and persist to the end of our simulations, ~5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with interactions than previously though.