Polar-ring galaxies in the Illustris TNG50 simulation

Abstract

ABSTRACT Polar-ring galaxies (PRGs) are an outstanding example of galaxies with misaligned kinematics where a typically red central galaxy is surrounded by a large-scale ring or disc of stars, gas, and dust oriented almost perpendicular to the main body. It is believed that polar structures (PSs) are formed in a secondary event after the assembly of a central galaxy, but due to their scarcity, their formation paths are not well constrained yet. We present a study of PRGs from TNG50 cosmological simulations, focusing on the origin of their PSs. Based on the synthetic images and baryonic mass distribution, we found six galaxies with stellar polar rings. Using Supplementary Data Catalogues and available particle data, we confirm that the selected galaxies are direct analogues of real PRGs. In our sample, the PSs are a result of the close interaction between the host galaxy and its companion. We track two formation paths for the stellar polar rings in our sample: (i) star formation in the accreted gas and (ii) tidal disruption of the satellite’s stellar component. Rings formed during the first scenario are, on average, bluer and younger than ones formed due to the satellite disruption. We report a steady increase of the ring’s inclination around the two most massive galaxies across a few billion years with a rate of ≈8° Gyr−1. The formation of a PS in some cases can increase the nuclear activity of the central galaxy and/or turn the active nucleus off completely.