The Identification of Asymmetric Barred Galaxies in Illustris TNG-50

TL;DR

This study classifies barred galaxies in the TNG50 simulation into symmetric and asymmetric types, revealing that asymmetric bars are more common in less massive galaxies with higher gas densities and star formation.

Contribution

It introduces a classification of barred galaxy morphologies in TNG50 and analyzes their physical properties, highlighting the prevalence and characteristics of asymmetric bars.

Findings

Asymmetric bars are more common in less massive galaxies.

Galaxies with asymmetric bars have higher gas densities and star formation.

Asymmetric bars tend to form earlier and may evolve into symmetric bars.

Abstract

Most barred galaxies exhibit symmetric structures. However, recent studies have shown that a subset of barred galaxies exhibit lopsided morphologies. To quantify their occurrence and investigate their physical origins, we analyze barred galaxies in the IllustrisTNG TNG50 simulation. We select 519 clearly barred galaxies in their stellar mass maps out of 770 barred galaxies from the TNG50-1 catalog. We classify the bar morphologies into four subgroups - `Lopsided', `Perturbed', `Symmetric', and `Indeterminate' - and perform a comparative analysis of their physical properties. We find that galaxies hosting asymmetric bars (`Lopsided' and `Perturbed') tend to have higher gas densities around the bar region, enhanced star formation activity, and more recent bar-formation epochs than galaxies with symmetric bars. However, the factor that most consistently distinguishes the four subgroups is the stellar mass distribution of the host galaxy, and there appears to be no physical correlation with bar size. These findings suggest that asymmetric bars form preferentially in less massive galaxies and may evolve into symmetric bars over time through secular processes. However, this conclusion should be considered with caution, as the fraction of asymmetric bars in the TNG50 simulation is systematically higher than that observed in the local universe.