Polar rings dynamics in the triaxial dark matter halo

TL;DR

This study combines spectroscopic observations and hydrodynamic simulations to analyze the dynamics and stability of polar rings in two galaxies within triaxial dark matter halos, constraining halo shapes and evolution.

Contribution

It provides new constraints on dark halo shapes and demonstrates the quasi-stability and evolution of polar rings through combined observational and simulation approaches.

Findings

Dark halo potential has specific semi-axis ratios for each galaxy.

Polar rings are dynamically quasi-stable over several billion years.

Spiral structures can grow and evolve into lopsided gaseous systems in polar rings.

Abstract

Spectroscopic observations at the Russian 6-m telescope are used to study the two polar ring galaxies (PRGs) from the catalogue by Moiseev et al.: SPRC-7 and SPRC-260. We have analyzed the kinematics of the stellar component of the central galaxies as well as the ionized gas kinematics in the external ring structures. The disc-halo decomposition of rotation curves in two perpendicular directions are considered. The observed 2D velocity fields are compared with the model predictions for different dark halo shapes. Based on these data, we constrain that for potential of DM halo semiaxis ratios is $s=0.8$, $q=1$ for SPRC-7 and $s=0.95$, $q=1.1$ for SPRC-260. Using 3D hydrodynamic simulations we also study the dynamics and evolution of the polar component in the potential of the galactic disc and dark halo for these two galaxies. We show that the polar component is dynamically quasi-stable on the scale of $\sim10$ dynamical times (about a few Gyr). This is demonstrate the possibility for the growth of a spiral structure, which then steadily transforms to a lopsided gaseous system in the polar pane.