The origin of lopsidedness in galaxies

TL;DR

This paper investigates the causes of lopsidedness in disc galaxies by simulating three mechanisms—flybys, gas accretion, and ram pressure—and compares the results with observations, suggesting flybys as a primary cause.

Contribution

The study compares three mechanisms inducing lopsidedness in galaxies through simulations and observational data, highlighting flybys as a significant contributor.

Findings

Flybys can account for approximately 20% of lopsided galaxies.

All three mechanisms can induce gaseous lopsidedness in disc galaxies.

The case of NGC 891 supports a flyby origin for its lopsidedness.

Abstract

It has long been known that a large fraction of disc galaxies are lopsided. We simulate three different mechanisms that can induce lopsidedness: flyby interactions, gas accretion from cosmological filaments and ram pressure from the intergalactic medium. Comparing the morphologies, HI spectrum and m=1 Fourier components, we find that all of these mechanisms can induce lopsidedness in the gaseous component of disc galaxies. In particular, we estimate that flybys can contribute to ~20 per cent of lopsided galaxies. We compare our simulations with the observations of NGC 891, a lopsided, edge-on galaxy with a nearby companion (UGC 1807). We find that the main properties of NGC 891 favour a flyby event for the origin of lopsidedness in this galaxy.