Streams in the Aquarius stellar haloes

TL;DR

This study uses high-resolution cosmological simulations to analyze the distribution of stellar streams in galaxy haloes, revealing a rich substructure that can be identified in velocity and conserved quantities, with implications for understanding galaxy formation.

Contribution

It demonstrates the prevalence and properties of stellar streams in simulated galaxy haloes, highlighting the impact of resolution and chaotic mixing on substructure detection.

Findings

Number of streams ranges from 300 to 600 in local volumes.

Up to 84% of particles are linked to stellar streams.

Stream count decreases with galactocentric radius.

Abstract

We use the very high resolution, fully cosmological simulations from the Aquarius project, coupled to a semi-analytical model of galaxy formation, to study the phase-space distribution of halo stars in "solar neighbourhood"-like volumes. We find that this distribution is very rich in substructure in the form of stellar streams for all five stellar haloes we have analysed. These streams can be easily identified in velocity space, as well as in spaces of pseudo-conserved quantities such as E vs. Lz. In our best-resolved local volumes, the number of identified streams ranges from ~ 300 to 600, in very good agreement with previous analytical predictions, even in the presence of chaotic mixing. The fraction of particles linked to (massive) stellar streams in these volumes can be as large as 84%. The number of identified streams is found to decrease as a power-law with galactocentric radius. We show that the strongest limitation to the quantification of substructure in our poorest-resolved local volumes is particle resolution rather than strong diffusion due to chaotic mixing.