Old stellar counter-rotating components in early-type galaxies from elliptical-spiral mergers

TL;DR

This study uses numerical simulations to explore how major mergers between elliptical and spiral galaxies can create old stellar components that rotate counter to the galaxy's main rotation, highlighting the role of disk preservation and tidal forces.

Contribution

It demonstrates that counter-rotating stellar components can form in both dissipative and dissipationless mergers, emphasizing the importance of the disk component and tidal interactions.

Findings

Counter-rotation can occur in both dissipative and dissipationless mergers.

The disk component tends to preserve its initial spin, contributing to counter-rotation.

Tidal forces transfer orbital angular momentum to the outer regions of the galaxies.

Abstract

We investigate, by means of numerical simulations, the possibility of forming counter-rotating old stellar components by major mergers between an elliptical and a spiral galaxy. We show that counter-rotation can appear both in dissipative and dissipationless retrograde mergers, and it is mostly associated to the presence of a disk component, which preserves part of its initial spin. In turn, the external regions of the two interacting galaxies acquire part of the orbital angular momentum, due to the action of tidal forces exerted on each galaxy by the companion.