Lopsided Galaxies in a cosmological context: a new galaxy-halo connection

TL;DR

This study investigates the origins of lopsided features in disc galaxies using cosmological simulations, revealing correlations with galaxy properties and dark matter halo characteristics, and suggesting a strong galaxy-halo connection rather than satellite interactions.

Contribution

It provides new insights into the physical conditions and dark matter halo properties associated with lopsided galaxies, highlighting the galaxy-halo connection in a cosmological context.

Findings

50% of galaxies have significant lopsided modes

Lopsided galaxies have lower central densities and more extended discs

Dark matter halo asymmetry and high spin correlate with lopsidedness

Abstract

Disc galaxies commonly show asymmetric features in their morphology, such as warps and lopsidedness. These features can provide key information regarding the recent evolution of a given disc galaxy. In the nearby Universe, up to $\sim30$ percent of late-type galaxies display a global non-axisymmetric lopsided mass distribution. However, the origin of this perturbation is not well understood. In this work, we study the origin of lopsided perturbations in simulated disc galaxies extracted from the TNG50 simulation of the IllustrisTNG project. We statistically explore different excitation mechanisms for this perturbation, such as direct satellite tidal interactions and distortions of the underlying dark matter distributions. We also characterize the main physical conditions that lead to lopsided perturbations. 50 percent of our sample galaxy have lopsided modes $m=1$ greater than $\sim 0.12$. We find a strong correlation between internal galaxy properties, such as central stellar surface density and disc radial extension with the strength of lopsided modes. The majority of lopsided galaxies have lower central surface densities and more extended discs than symmetric galaxies. As a result, such lopsided galaxies are less self-gravitationally cohesive, and their outer disc region is more susceptible to different types of external perturbations. However, we do not find strong evidence that tidal interactions with satellite galaxies are the main driving agent of lopsided modes. Lopsided galaxies tend to live in asymmetric dark matter halos with high spin, indicating strong galaxy-halo connections in late-type lopsided galaxies.