On the identification of substructure in phase-space using orbital frequencies

TL;DR

This paper demonstrates that orbital frequency space is highly effective for identifying and dating past merger events in galaxy evolution, even in complex, evolving systems.

Contribution

It shows that orbital frequency space reliably reveals merger streams and their ages in both idealized and realistic N-body galaxy simulations.

Findings

Streams are easily identifiable in frequency space.

Separation of streams correlates with time since accretion.

Features are preserved in evolving gravitational potentials.

Abstract

We study the evolution of satellite debris to establish the most suitable space to identify past merger events. We confirm that the space of orbital frequencies is very promising in this respect. In frequency space individual streams can be easily identified, and their separation provides a direct measurement of the time of accretion. We are able to show for a few idealised gravitational potentials that these features are preserved also in systems that have evolved strongly in time. Furthermore, this time evolution is imprinted in the distribution of streams in frequency space. We have also tested the power of the orbital frequencies in a fully self-consistent (live) N-body simulation of the merger between a disk galaxy and a massive satellite. Even in this case streams can be easily identified and the time of accretion of the satellite can be accurately estimated.