Pattern speeds in interacting galaxies

TL;DR

This study examines how spiral patterns in interacting galaxies have variable pattern speeds that decrease with radius, differing between stellar and gaseous components, challenging the notion of a single pattern speed.

Contribution

It provides detailed modeling of pattern speeds in interacting galaxies, showing they are not unique and vary with radius and component type.

Findings

Pattern speed decreases with radius in simulated interacting galaxies.

Stellar components exhibit higher maximum pattern speeds (~20 km/s/kpc).

Gas components have consistently low pattern speeds (~5 km/s/kpc).

Abstract

We investigate pattern speeds in spiral galaxies where the structure is induced by an interaction with a companion galaxy. We perform calculations modeling the response of the stellar and/or gaseous components of a disc. Generally we do not find a unique pattern speed in these simulations, rather the pattern speed decreases with radius, and the pattern speed for individual spiral arms differ. The maximum pattern speed is ~20 km/s/kpc for the discs with a live stellar component, decreasing to 5 km/s/kpc at the edge of the spiral perturbation. When only the gas is modeled, Omega_p is typically very low (5 km/s/kpc) at all radii.