Peculiar galaxies I: A Catalog of Polar-Ring Galaxies from the TNG50 Simulation

TL;DR

This paper uses the TNG50 simulation to identify and analyze 32 polar ring galaxies, revealing their properties and differences from observed counterparts, to better understand their formation and structure.

Contribution

First comprehensive catalog of simulated polar ring galaxies from TNG50, analyzing their properties and morphological diversity.

Findings

Sample exhibits properties similar to observed PRGs.

Rings are less massive and slightly less perpendicular than observed.

Host galaxies are mostly early-type with diverse morphologies.

Abstract

The hydrodynamic cosmological simulation, TNG50, is employed to conduct an analysis of multi-spin galaxies that exhibit ringed structures composed of gas and stars that orbit nearly perpendicular around a host galaxy, known as polar ring galaxies (PRG). To ensure a robust sample, we select subhalos based on the angle subtended by the angular momentum profiles, as well as on a visual inspection. The analysis is focused on galaxies with stellar masses greater than 10$^{9}$ M$_\odot$. In addition, a dynamic decomposition is employed to separate the stellar and gaseous ring from the host galaxy. This results in a sample of 32 subhalos with PRGs. This sample exhibits properties similar to those observed. These include colours typical of early-type galaxies (ETGs) or those transitioning toward blue systems. Most host galaxies are classified as ETGs, with 37.5\% exhibiting a disk-dominated morphology. The mean bulge-to-total (B/T) ratio is 0.64. Rings have average radii that are 2.36 and 3.41 times larger than their effective radii for the stellar and gaseous components, respectively, with star formation occurring predominantly within the rings. In contrast with observations, rings in the simulation tend to be less massive and slightly less perpendicular. The obtained sample displays a variety of host galaxy morphologies, including wide and narrow rings, providing a robust framework for studying the varied structural characteristics of PRG variants.